
Class b 

Book 

Gopyright^ . 



COPYRIGHT DEPOSIT 



DENTAL 
RADIOLOGY 



BY 



FRANCIS LE ROY SATTERLEE, Jr., A. M., D. Sc. 

w 

ASSISTANT TO THE PROFESSOR OF PHYSICS, CHEMISTRY AND METALLURGY ; 

LECTURER ON PHYSICS; LECTURER ON RADIOLOGY; DIRECTOR OF PRACTICAL 

PHYSICS LABORATORY; DIRECTOR OF X RAY LABORATORY; CHIEF OF 

X RAY SECTION OF THE CLINIC ; NEW YORK COLLEGE OF DENTISTRY. 



PUBLISHED BY 

SWENARTON STATIONERY COMPANY 

PRINTERS AND PUBLISHERS 

121 East 27th Street 
New York, N. Y. 






Copyrighted, 1913 
FRANCIS LE ROY SATTERLEE, Jr. 



*9 



<y< 



©CI.A358G77 



TABLE OF CONTENTS 

PAGE 

INTRODUCTION 7 

CHAPTER I. 

Early Investigations and Discovery of the X Ray 13 

CHAPTER II. 

The Complete Spectrum — Invisible Rays — The Rays Com- 
prising the Study of Radiology — General Properties 19 

CHAPTER III. 

Ultra Violet Rays, Their Nature, Characteristics and 
Applications 25 

CHAPTER IV. 

Bi-ultra Violet Rays, Their Nature, Characteristics and 
Applications 29 

CHAPTER V. 

Tri-ultra Violet Rays, Their Nature, Characteristics and 
How Generated in a Vacuum Tube 33 

CHAPTER VI. 

The X Ray Tube 43 

CHAPTER VII. 

Symptoms of High and Low Vacuum — Remedies for Same.. 53 

CHAPTER VIII. 

The Essentials of an Outfit — Methods of Generating High 
Potential Electric Currents — Electrical Measurements.... 59 

CHAPTER IX. 

Electrical Induction — Construction of X Ray Coils 73 

CHAPTER X. 

The Interrupter — Tube Shields — Valve Tubes — Wiring 
Diagrams 83 

3 



TABLE OF CONTENTS— Continued 

CHAPTER XL PAG E 

The Film and Its Preparation 95 

CHAPTER XII. 

Application of the Principles of Shadows, to Avoid 
Distortion 99 

CHAPTER XIII. 

Technique of Taking the Picture 107 

CHAPTER XIV. 

Development and Mounting of Negatives 119 

CHAPTER XV. 

Head Pictures on Plates 127 

CHAPTER XVI. 

Dangers of the X Ray 131 

CHAPTER XVII. 

Reading the Negatives 177 

CHAPTER XVIII. 

Diagnosis of Pathological Conditions 181 

CHAPTER XIX. 

Stereoscopic Radiographs of the Teeth 191 

CHAPTER XX. 

Conclusion 195 



PREFACE 

The author desires to express his sincere thanks for sug- 
gestions, information or the use of cuts from the following: 

Mr. Irwin Howell, of the General Electric Co. 
The American X Ray Equipment Co. 
The Wappler Electric Mfg. Co. 
MacAlaster & Wiggin Co. 
Waite & Bartlett Co. 

Since this book is written primarily as a text book for the 
undergraduate dental student, to be used in the laboratory, and 
while attending clinical lectures, blank pages have been 
inserted between the chapters to facilitate the student in the 
taking of additional notes, and to insure their proper preserva- 
tion associated with the subject to which they belong. 

It is earnestly hoped by the author that all students will 
take advantage of these note pages while attending lectures. 

Any suggestions or criticisms, favorable or otherwise, will 
be welcomed by the author. 



Francis L£ Roy Satt£rl££, Jr. 

148 East 18th Street 

New York City August 1, 1913 



INTRODUCTION 

What Radiology Means to You — A 
Plain Talk with the Undergraduate 



What real value is Radiology to the dentist? That is a 
question that is being answered every day by one's own practice, 
although sometimes the practitioner ignores or does not under- 
stand the answer. Some of you are willing to work along in 
the same old rut and not attempt to utilize the advantages of the 
recent discoveries in modern science, until you become back 
numbers; and then take them up only because you are afraid 
to be elected in the "fogy" club if you do not. Others rush 
ahead heedlessly into fields unknown, without blazing any trail, 
with the result that suddenly they realize that they are in a 
wilderness and hopelessly lost. Which is the greater of these 
two evils is hard to say, but I think, of the two, the last man 
has the best chance to succeed, since some friend may happen 
to come along at the moment he is beating around looking for 
the trail and "lead him to it." But the really successful man 
is he who goes through life with his eyes open, his ears open, 
and his mouth shut; his hands out ready to grasp anything new 
that comes along; to inspect it, study it, and, if it appears to 
be at all useful to him, to store it away in his brain with a tag 
"keep forward" on it; ever ready to take it out and refer or 
add to it, till, at length, he has developed a subject full of 
interest and usefulness, that has been matured and ripened into 
an established and working rule or adjunct of his profession. 

This is the man who to-day will be able to answer the 
question I first put to you, and he will tell you many things 



you little dreamed of. He will tell you first that the subject of 
Dental Radiology embraces quite a field, the one part of which 
has been well cultivated, while the other part is more or less 
barren. The cultivated part he will tell you is that part of the 
subject which deals with the X Ray as a diagnostic agent; the 
uncultivated part being the use of the X Ray as a therapeutic 
agent. If he is truthful, he will probably add that he does not 
mean to disparage the latter subject, but only wishes to profess 
unfamiliarity with it, although looking forward to future de- 
velopments. You will probably ask this sensible man, if you 
are really seeking enlightenment, what he has found in the 
X Ray to be of any benefit to him and how? He may look at 
you with a supreme smile of pity and tell you to open your 
eyes and test it yourself, or he may try to explain some of 
the uses of the ray to you. If he is very generous and willing 
to help you along, and has, besides some leisure time, he will 
take you to his office and show you some of the recent cases 
that he used the X Ray on, and with what results. You will 
take out your note book and will make notes something like this : 
"X Rays used with good success in cases of impacted 
teeth, non-erupted and supernumerary teeth, regulating cases. 
Fractures of the teeth and the maxilla, inspecting and measuring 
curved roots and canals, pulp stones, exostosis, secondary den- 
tine, small pulp chambers, length and condition of root fillings, 
foreign bodies in the canals, old roots left after extraction, 
faulty bridge work, pericementitis, alveolar abscess, empyema of 
the antrum locating the position of abnormal antra, necrosis, 
absorption of alveolus subsequent to old age or extraction of 
teeth, chronic fistulas, pyorrhea, showing the amount of absorp- 
tion in order to determine whether the prognosis is good for 
contemplated treatment, epulis, osteomas, odontomas and tumors 
of the oral cavity in general." When you have finished putting 
down this list you will probably think that there are not many 
conditions left to the dental surgeon. And you will wonder 
whether all this is true. Your friend, if he has had much 
experience, will turn to his card index of radiographs and take 



out picture after picture with appended history, and show you 
cases of each one of the pathological conditions he has enu- 
merated to you, and your doubt will turn to wonder. On the 
other hand, you may not be so lucky in finding as good a friend 
who will give up his time in explaining to you the advantages 
of the X Ray, but will let you go your way in blissful ignorance 
of the value of so useful an agent. 

While you are in college you will have a short course in 
Radiology that will interest you for the time being, but which 
interest, in all probability, will be absorbed in the general rush 
and scramble to get through college ahead of your fellow class- 
man with the least possible study and with the highest honors, 
giving time only to what you consider will be your hard subjects 
when you come to the final spurt for the much coveted D. D. S. 
You will attain this ; subsequently, you will pass your State 
Board; and eventually you will, with the greatest of pride and 
considerable swelling of the chest and head, hang out your 
shingle in a part of the community where you think you will 
have more chance than your neighbor to rapidly acquire a 
practice, and reap a golden harvest. Your ambition may per- 
haps be realized at once, but alas ! fate seems to have, in the 
majority of cases, decreed otherwise; and the chances are that 
you will have often to sit alone in your office waiting for the 
expected patients, and look out of the window only to see the 
steady* stream of patients passing up the stoop of the house 
opposite, where Dr. Blank lives. You will then, if you are at 
all human, feel the first qualms of envy and you will ponder 
why it is Blank has such a good practice. You will say to 
yourself that he is a young man, too, and only graduated a 
few years ago, and you will fail to understand what great 
power he has that you do not possess. You will then sit down 
and read the dental journals, and try to improve your educa- 
tion and polish off the rough work as it came through the 
mill of your college career. Then it is that your thoughts may 
for the first time go back over your years at college, and you 
will think of your Radiology course, and remember the interest 




it awakened in you at that time. This may even be brought 
to your mind by several articles on X Ray in the current 
journals. You will wish your course had been longer, and you 
will dig out your old and now-forgotten note books and you 
will find a very few notes on the subject, and you will wish, / 
know you zvill (many others have, and they have told me so), 
that you had only given the subject more attention and had 
taken more notes when you had the opportunity. You will 
hunt through your journals and you will probably discover 
some very interesting article on the subject, although somewhat 
out of your depth, and behold! you may even find one by your 
now much-hated rival, Blank, from across the street. 

All this may happen, and again it may not occur at all. 
On the other hand, you may go years without more than a 
lingering occasional thought to the subject, but the time will 
come eventually ! Just as surely as the profession has advanced 
to what it is, so surely will the time come when every dentist 
will have to admit Radiology as an integral and necessary part 
of his profession. This is no idle prophecy built on air castles, 
or the outcome of an enthusiastic desire to see it so ; but I 
assure you, these statements are based on facts ; and sta- 
tistics will bear me out in showing the ever-growing demand 
for radiographs made on the specialist by the dentist; and the 
wonderful increase in the sales of the manufacturers of dental 
apparatus for X Ray work. It is for this reason that I am 
urging one and all of you to give the matter some thought and 
go out from your Alma Mater with some idea of the value of 
one of the most wonderful and useful weapons nature has given 
the modern dentist with which to fight against the difficulties 
and doubts that must arise in your work. Not only do I ask 
you to understand the subject, but I ask you individually to 
make one trial of its value on the first case you have occasion 
for it in your practice, and to judge for yourself whether or 
not what I say is true. You do not have to instal a complete 
set of apparatus in your office to do this ; you can send the 
case to a specialist who will, within twenty-four hours, send you 

10 



a finished radiograph to study and determine the course of 
treatment. Do you think it is right to ignore the possibility 
of proving the exact conditions of a doubtful case? Is it just 
to yourself and your patient not to take every means within 
your power to ascertain the true condition of their case before 
you proceed to operate? 

Answer these questions in the negative, and you will per- 
haps discover why your rival Blank has been so very successful. 



11 



NOTES 



12 



CHAPTER I. 
Early Investigations and Discovery of the X Ray 

Michael Faraday was the pioneer investigator of electrical 
currents and vacuum tubes. As early as 1838 he conducted a 
series of experiments with an electrical discharge through rari- 
fied gases, and invented the terms 'anode' and 'cathode' for 
positive and negative electrodes. His researches are now his- 
torical, inasmuch as they opened up a new field of investigation 
that was in time to bear fruit in the marvelous, though acci- 
dental, discovery of the X Ray. 

Faraday was followed some time later by Gassiott, whose 
ideas were afterward carried out by Geissler, of Bonn, the first 
to construct the tubes that now bear his name. 

Up to this time the investigations proved but little of 
importance, beyond the fact that any rarified gas gave off 
a peculiar glow, or phosphorescence, when subjected to an 
electrical discharge of high potential. This phenomenon became 
known as 'fluorescence: Air produced a pale violet glow, 
hydrogen a red, and carbon dioxide a steel-blue shimmer. 

Professor Hittorf, the celebrated electrical physicist, of 
Munster, next experimented with a Geissler tube of higher 
degree of exhaustion. He noticed an increasing resistance of 
the electrical current to the coefficient of rarification, he also 
found that the color of the gases under fluorescence varied 
with this increased degree of rarification and that the glow 
proceeded in straight lines from the negative electrode, casting 
a shadow of an interposed object upon the wall of the tube, 
and he furthermore disclosed the fact that these rays were 
capable of deflection by a magnet. 

Doctor Crooks, afterward Sir William, was the next inves- 
tigator to enter the field of research, and in 1878 made some 

13 



interesting announcements that did a great deal toward popu- 
larizing the subject. He experimented with the rectilinear 
rays of the Hittorf tube and devised the theory that the 
rectilinear path was caused by the current attaching itself to 
freely moving molecules of gas as it left the cathode, and 
proceeded in parallel lines with great velocity, and bombarded 
the opposite side of the tube, or other intervening object, with 
terrific impact. Sir William Crooks also succeeded in focusing 
these rays of rapidly moving molecules by curving the cathode, 
thus giving to it the form of a concave mirror, and thereby 
projecting the rays to a common point, instead of in parallel 
lines. Objects placed at the focus of these rays were heated 
to whiteness. This was supposed by Doctor Crooks to be 
caused by the bombardment from the enormous quantity of 
projected molecules. 

Simultaneously with this announcement by Sir William 
Crooks, M. Goldstein came forward with the theory that the 
phenomenon was caused by a transmission of energy, and not 
by the bombardment with actual particles; but he could not 
give any definite explanation of his 'transmitted energy.' 

Professor Weidemann, of Leipsic, in 1883, was the first 
to ascribe to the "Cathode Rays," as they began to be called 
because they emanated from the cathode electrode, the possi- 
bility that they were in reality light waves of extremely short 
wave-length at the remote end of the spectrum, far beyond the 
violet rays. Paul Lenard, a pupil of the famous Professor 
Hertz, also believed in this hypothesis, and in a series of 
experiments conducted at Bonn, proved conclusively that there 
was not only evidence of cathode rays outside of the generating 
Hittorf's or Crooks' tube, but that, furthermore, the rays even 
penetrated a thin sheet of aluminum foil, a fact that none of 
the investigators previous to this had ever suspected. 

Prof. J. J. Thompson, of the Cavendish Laboratory at 
Cambridge, by an ingenious method afterward succeeded in 
actually measuring the velocity of these cathode rays, which 
he approximated to be about 200 kilometers, or about 124 

14 



miles, a second. It might be well to mention in reference to 
Professor Thompson that he advocated still another theory in 
regard to the nature of the cathode rays, similar to, yet differ- 
ing from that of Crooks , namely that the molecule of electric- 
ally charged gas, or atmosphere, splits up into two or more 
'ions.' This term, meaning 'traveler,' was so named by 
Faraday who has added largely to the nomenclature of 
electrical science, a term which, however, had long been used 
in connection with such electrically charged portions of matter 
as were known to exist in the passage of a current of electricity 
through a liquid. 

After a long period of dormancy following the assertions 
of Paul Lenard, the world was once more aroused, in the year 
1895, by the proclamation of Prof. Wilhelm Conrad Rontgen, 
that he had discovered an entirely new ray differing from 
any of the cathode rays that had formerly existed. 

Like many other great discoveries, it was brought about 
through the accidental grouping of apparatus and conditions 
that were just ripe to disclose to the unsuspecting investigators 
facts that had been taking place time and again unobserved and 
unrecorded. In many cases it has taken but a simple incident 
to disclose to the ever receptive and gifted minds of our great 
inventors a new truth that has existed for untold years, and 
needs but the spark of intellect to develop and fan into life 
a new wonder that would in time revolutionize its own field 
of application. 

So it was that Professor Rontgen, while experimenting 
with a Hittorf tube of high vacuum accidentally stumbled upon 
a discovery so remarkable and unbelievable at first, that 
scientists and laymen alike, from every quarter of the globe, 
paused in their daily occupations and gazed with amazement 
and incredulity at the first printed and brief reports of this 
most wonderful discovery. "A new ray had been discovered 
by means of which it was possible to look through opaque 
substances !" 

15 



Authenticated and more detailed reports were soon pro- 
mulgated, and it developed that another instance had occurred 
where accidental grouping of conditions had born fruit little 
suspected by the now renowned investigator. The conditions 
were these: Rontgen had covered his vacuum tube with black 
cardboard. He had also coated another piece of cardboard with 
the crystals of barium-platino-cyanide, which he was testing 
for its fluorescence under cathode rays. This fluorescent 
'screen' he had placed against a table in his laboratory to dry 
on the opposite side of the room from the vacuum tube. Then 
to test the tube he turned out the lights and switched on 
the current, passing the high potential discharge through the 
Hittorf tube covered with black cardboard. He then suddenly 
became aware of the fact that the barium-platino-cyanide screen 
was glowing brilliantly on the other side of the room, and 
furthermore in crossing the room to examine it, he passed 
between the covered tube and the screen, and was amazed to 
find that a shadow was cast upon the screen ! It was only 
this that was needed to set this experienced investigator 
directly upon the correct solution of the apparent mystery. He 
at once suspected that a new ray had been found that had 
penetrated the black cardboard covering of his tube and affected 
the screen. He now turned the screen around with its card- 
board back toward the tube. The fluorescence still continued 
on the crystal-coated side. The new ray had also penetrated 
through* the back of the screen. He next took a large book of 
a thousand pages or more, and held it between the screen and 
the covered tube; still the glow persisted. The climax was 
reached when on holding his own hand between the tube and 
the screen he saw to his utter amazement depicted before him 
the complete shadowgraph of his hand, and more wonderful 
yet, the bones were outlined in solid black through the less 
dense flesh of the hand ! 

He further discovered that these unknown rays had an 
active influence on a photographic plate, and that shadowgraphic 

16 



pictures of the bones of the hand could be obtained in this 
manner. 

This revelation was received by the scientific world with 
intense interest, and the enthusiasm of the medical profession 
was henceforth enlisted. 

In Professor Rontgen's original communication to the 
Wurzburg Physico-Medical Society, dated December 1895, he 
describes some of his experiments and the conclusions that he 
deduced from them. Among other things he showed that the 
rays were not polarizable, nor could they be reflected, conse- 
quently he found that they could not be concentrated by 
lenses. He also discovered that the transparencies of different 
bodies under these rays depended entirely upon their density. 

He gave to these wonderful and mysterious rays the name 
of the algebraic unknown quantity 'X,' and by this name, 
it is known to-day, notwithstanding the subsequent classi- 
fications of the ray and the bestowing upon it of a more 
accurate and dignified appellation. X Rays they were known 
as, and to the vast army of experimenters that have taken up 
their investigations X Rays they will always remain, an excel- 
lent example of how a popular misnomer may find its way into 
the nomenclature of scientific literature. 

Professor Rontgen concluded his original paper with the 
hypothesis that these new X Rays were perhaps due to longi- 
tudinal vibrations of the ether. 

Since that date there have been a large number of investi- 
gators in the field, many of whom have advanced some 
hypothesis or another concerning the exact nature of Rontgen's 
X Rays, but the old theory that Professor Weidemann brought 
forward in 1883, in reference to the cathode rays, was applied 
to the Rontgen radiation and is now the only explanation that 
has survived the critics of the scientific world. 

We will now consider this present theory regarding the 
nature of the 'Rontgen Rays.' 



17 




THE COMPLETE SPECTRUM 



TRI- ULTRA -RED. 
WAVE LENGTH - (VERY LONG.) 



BI- ULTRA -RED. 
WAVE LENGTH - 18 MICRONS. 

(ELECTRICITY.)) 



Heat 
Ray: 



-< 



Optical 
Rays. 



RED. 
WAVE LENGTH - .71 MICRON. 



ORANGE. 
WAVE LENGTH - .66 MICRON. 



YELLOW. 

WAVE LENGTH - .62 MICRON. 



GREEN. 
WAVE LENGTH - .53 MICRON. 



BLUE. 
WAVE LENGTH - .49 MICRON. 



INDIGO. 
WAVE LENGTH - .41 MICRON. 



VIOLET. 
WAVE LENGTH - .38 MICRON. 



ULTRA-VIOLET. 
WAVELENGTH - .21 MICRON. 



BI- ULTRA -VIOLET. 
WAVE LENGTH - . I MICRON. 



TRI -ULTRA -VIOLET. 
WAVE LENGTH - .014 MICRON. 



V Chemically 
\ Active 
( Rays. 



Finsen 
Ravs 



Figure 1 — (see page 19) 



IS 



CHAPTER II. 

The Complete Spectrum — Invisible Rays — The Rays Comprising the 
Study of Radiology — General Properties 

Figure 1 represents a diagram of the complete spectrum. 
You have probably from your physics associated the spectrum 
with the seven primary colors, viz. : violet, indigo, blue, green, 
yellow, orange and red, but the complete spectrum shows the 
presence of rays, both above the red and below the violet. The 
three rays above the red receive their names from their relation 
to the nearest visible ray, which is red : the first is called ultra 
red (meaning "beyond the red"), next, we have the bi-ultra 
red (meaning "twice beyond"), and in the same manner tri- 
ultra red indicates a group of rays that is still further removed, 
and might therefore be considered as three times beyond the 
physical red ray.* 

Between the ultra red and bi-ultra red divisions there exists 
a break in the spectrum. Just what group of rays belong in 
this space we have so far been unable to determine, although 
the theory has been advanced that all electrical phenomena 
occupy this gap. This very likely hypothesis will never be 
proved until we are able to determine, with some degree of 
accuracy, the wave-length of electricity. 

The ultra red rays are heat rays. The entire phenomena 
of heat are grouped in this division. They are invisible to the 
eye and their presence is known only by their effects, which 
are thermal in nature. Just above the break we have the 
bi-ultra red or magnetic rays. That part of physics which we 
know under the general term of 'magnetism' is included as 
belonging to this group, or division, of the spectrum. 



* This nomenclature, "bi-ultra" and "tri-ultra," was suggested by the author in 
1904 to take the place of the terms "ultra-ultra" and "ultra-ultra-ultra." See 
Medical Record of January 16, 1904 — "The Rontgen or Tri-ultra Violet Rays, Their 
Nature, Applications, and Dermatological Effects." 

19 



Above the bi-ultra red comes the tri-ultra red, or those 
long rays of the ether, called Hertzian rays, now utilized in 
wireless telegraphy. 

In all probability we have the following sequence: starting 
with the visible rays of red, which are to a certain extent heat 
rays, there is a shading off gradually to the invisible rays of 
heat, which are termed ultra red. Again we have a shading 
off from the pure effects of heat to the thermo-electrical 
phenomena. Then probably to the pure electrical phenomena, 
which are supposed to occupy the break above the ultra red 
rays, then to the electro-magnetic phenomena as we approach 
the bi-ultra red. Next the phenomena of pure magnetism, then 
those long magnetic rays of the ether, and finally the longest 
non-magnetic Hertzian or tri-ultra red rays. 

The only difference between any of the rays in the complete 
spectrum, from the tri-ultra red at the top to the tri-ultra violet 
at the bottom, is the wave-length. If we had any means of 
changing the wave-length of one ray to that of another, we 
would also change its characteristics, for example (the wave- 
lengths are given on the diagram under their names), take 
the orange ray with the wave-length of .66 of a micron (a 
micron equals one millionth of a meter), and suppose we had 
some means of shortening this wave-length to, we will say, 
.014 of a micron, we would then change the orange ray into 
the tri-ultra violet. The orange ray would lose its color, it 
would become invisible and it would take on the characteristics 
of the tri-ultra violet, or in other words it would be converted 
into the X Ray, with all the properties of the X Ray. With 
the means at present at our disposal it is impossible to make 
the change in this particular case, but there are some instances 
where we can change certain rays into certain other rays, as 
we will see later on. 

The tri-ultra red, or the Hertzian rays, are the longest of 
the spectrum rays and have no approximate wave-length. It is 
the only group of all the rays in the spectrum that varies to 
any great extent in wave-length, and it is to this fact that we 

20 



owe most of the improvements in wireless telegraphy. It makes 
it possible for an operator in one section of the country to 
communicate with any given station in any other part of the 
country, by turning his system to the same length of wave as 
that of the one which he wishes to call, thus securing selectivity 
in sending wireless messages. 

You will note from the diagram that the wave-length 
gradually decreases from the top as you go down toward the 
bottom of the spectrum. Starting with the longest rays of the 
tri-ultra red, we come next to the bi-ultra red of 18 microns; 
then the ultra red, 8 microns ; then the red rays, .71 of a 
micron; the orange, .66 of a micron; yellow, .62, and so on, 
till we get down to the ultra violet with a wave-length of .21 
of a micron. Below this we have a still shorter ray, the bi-ultra 
violet, with a wave-length of .1 of a micron, and finally, the 
shortest of all known rays, the tri-ultra violet, or the X Ray, 
with a wave-length of .014 of a micron. 

The three groups of rays that we have to consider under 
the general heading of Radiology, particularly in their applica- 
tion to Dentistry, are the ultra, bi-ultra and tri-ultra violet rays. 
We will consider first their general properties, that is, proper- 
ties that are common to them all, perhaps not to the same 
extent or to the same degree. Then we will consider them 
as to their specific properties , that is, the properties and 
characteristics that each one has in particular. 

The first general property to be considered is the pene- 
trative power. They all three have a certain penetrative power, 
and the extent to which each one has this property is governed 
by a law which we know as the "Law of Penetration." This 
may be formulated as follows: 

"The penetration varies inversely with the wave- 
length, and also with the density and thickness of the . 
substances to be penetrated." 

This means that the shorter the wave-length the greater 
the penetration, and conversely, the longer the wave-length the 
less the penetration. The ultra violet is the longest of the 

21 



three rays, it therefore has the least penetration. The tri-ultra 
violet or X Ray is the shortest, consequently it has the greatest 
penetration. Also the thicker and more dense the substance, the 
less readily will it be penetrated. Density and thickness, how- 
ever, are not the same thing. We can have a block of wood 
measuring one cubic inch; we can also have a block of lead with 
exactly the same volume, namely, one cubic inch. One is as 
thick as the other, but the lead is very much denser, as is shown 
by its specific gravity. The specific gravity is, therefore, the 
direct index for the density, and the greater the specific gravity 
the denser the substance, and the less readily will it be pene- 
trated by these three rays. 

Another general property of the three rays is their thera- 
peutic power, which varies to some extent and with different 
pathological conditions. These we will consider separately. 

The third general property is the chemically active power 
of the three rays. They all have the power of producing certain 
chemical changes or reactions in certain substances, not to the 
same extent, but inversely proportional to the wave-length. This 
property is not confined to these rays alone, but referring to 
the diagram we will see bracketed as the 'chemically active' 
rays, the tri-ultra violet to the red, inclusive. The red is the 
least chemically active and the tri-ultra violet the most. It is 
for this reason that we use a red light in the dark-room when 
manipulating photographic plates and films. The sensitive 
plate is not affected by the red light unless it be exposed to it 
for a long time. Since the red is so slightly chemically active 
it does not affect the sensitive emulsion of the plate or film 
by producing chemical changes in the salts. The orange is 
slightly more chemically active, and we can use it in the dark- 
room also, where we have a slower emulsion of plates and films, 
or where we have printing papers that are not as sensitive. 
The yellow and the green are a little more actinic or chemically 
active, while the blue is still more so. The indigo and the 
violet, and particularly the ultra violet, are also highly actinic. 
The bi-ultra violet is even more actinic, while the tri-ultra violet, 

22 



or the X Ray is the most actinic of all known rays. We can 
effect the sensitive emulsion on a photographic plate after the 
tri-ultra violet has passed through a block of wood ten or 
twelve inches thick, or even through a brick wall. 

Another general property of the rays which is closely 
allied to the chemically active power, is that power which the 
three rays have of producing fluorescence in certain substances. 
It is the phenomenon that results when we expose certain 
substances to these three rays, the substance giving off a peculiar 
glow which resembles phosphorescence, and which we call 
fluorescence. 



23 



NOTES 



24 



CHAPTER III. 

Ultra Violet Rays, Their Nature, Characteristics and Applications 

We will now consider each of these three rays separately. 
First, take the ultra violet, with a wave-length of .21 of a 
micron, the least penetrative of all these three rays. A single 
sheet of glass is sufficient to cut off absolutely all ultra violet 
radiation. The ray will not penetrate a substance with a 
density or specific gravity as great as glass. We therefore 
take 'glass' as the limit of penetration for the ultra violet ray. 
The ultra violet ray is produced in two ways : first, we find it 
in a free state, in the presence of an electrical spark. Under 
all circumstances and conditions, wherever we have an electrical 
spark, ultra violet rays are generated spontaneously. It makes 
no difference where the spark occurs, whether it is the spark 
that we find in an arc lamp, or whether it is the spark occurring 
in the spark-coil of an automobile, or whether it is the lightning 
that we see in the clouds; they are all sparks and they all 
produce ultra violet rays. It does not matter whether the spark 
takes place in the air or in a vacuum, except that in a vacuum 
the spark is invisible and takes place as a discharge or ionization. 
We do not use these ultra violet rays that are produced in 
the presence of a spark, except under rare circumstances, where 
we produce the spark with the intention of getting the ultra 
violet ray from it. In all other cases the ultra violet ray is 
thrown out on the atmosphere as an infinite radiation. We 
also find ultra violet rays directly in nature, in the presence 
of direct sunlight. A single pane of glass will cut off the 
ultra violet rays — we therefore have to have the sun's rays in the 
open and not coming through a glass window. It is supposed 
by some scientists that even these ultra violet rays come 
originally from an electrical spark, this spark taking place in 

25 



the atmosphere of the sun, as an ionization of the gases that 
envelop that planet. Of course this is only a theory and lacks 
the necessary proof, although the supposition seems plausible. 
The therapeutic effects of the ultra violet rays are very 
marked in tubercular conditions of the skin. The disease which 
is known as 'lupus vulgaris' yields most readily to ultra violet 
radiation. Doctor Finsen, of Copenhagen, Denmark, was one 
of the first to utilize this property of the ultra violet rays, and 
he did so in an especially constructed lamp. His apparatus 
consists first of a series or 'bank' of arc lights, the electrodes 
of which, instead of being constructed of carbon, as most arc 
lamps are that we use for illumination, are made of iron or 
copper, as he found that these two metals when used as 
electrodes gave off much richer radiations of ultra violet rays. 
These rays he collected by means of a parabolic mirror and 
concentrated them through a large telescope, the inverted end, 
or objective, of which was presented to the arc lamps. The 
lenses of this telescope were of peculiar construction; they 
could not be made of glass, as the ultra violet ray would not 
traverse them. He had to construct them of a substance that 
had a lesser specific gravity than glass, so he used quartz and 
colored it cobalt blue, which absorbed all the other light and 
heat rays of the spectrum, and allowed only the blue, indigo, 
violet and ultra violet rays to pass. You will see in Figure 1 
these four rays bracketed and classified as 'Finsen Rays.' The 
small end of the telescope was focused upon a patient who 
reclined on a couch below the apparatus, and these powerful 
rays, particularly those of the ultra violet, when allowed to 
radiate over a surface of lupus, caused a destruction of the 
tubercle bacilli and cured the lesion. The percentage of cures 
has been estimated to be as high as 97% of cases when treated 
with Finsen rays, and the only reason that it is not 100% is 
that we have to allow about 3% of failures due to faulty 
technique on the part of the operators, and also of the inability 
of patients to continue the prescribed treatments. 

26 



There are a number of other skin diseases for which the 
ultra violet ray also possesses a therapeutic value, but perhaps 
not to as great an extent as those shorter rays which we will 
now consider as the bi-ultra violet. 



27 



NOTES 



28 



CHAPTER IV. 
Bi-ultra Violet Rays, Their Nature, Characteristics and Applications 

The bi-ultra violet ray has a wave-length of .1 of a micron. 
It has a greater penetrative power than the ultra violet; it 
will pass quite readily through thin sheets of aluminum, one of 
the lightest of the metals, but will not pass through heavier 
metals. Aluminum is, therefore, the limit of penetration of 
these rays. 

Bi-ultra violet rays are obtained in two ways: — First, 
by the breaking up of the ultra violet into still shorter rays 
in the presence of a vacuum tube; and directly, in nature, 
in the presence of all radio active substances, such as radium, 
actinium, polonium, uranium and many others. These rays 
differ but very slightly from the ones generated in the vacuum 
tube, their characteristics are almost identical, and it is only in 
the wave-length which is slightly shorter that we note any 
distinction whatsoever. Bi-ultra violet rays are used quite a 
little in the treatment of superficial cases of cancer. They are 
also used to a very great extent when combined with currents 
of high frequency and high potential in the modern treatment 
of rheumatism; very good results can be obtained by this 
method. Cases of ankylosed and stiffened joints can be broken 
up and deposits of uric acid dissolved, but the best results are 
only obtained when a correct technique is used in the adminis- 
tration of the treatment, together with proper diet and alkaline 
medication. 

In dentistry we utilize the bi-ultra violet ray in the treat- 
ment of pyorrhea alveolaris, by means of the author's vacuum 
electrodes, especially designed for the purpose, with excellent 
results when the technique is carefully and faithfully carried 
out. 

29 



The therapeutic value of the rays given off by radium is 
so closely identified with the vacuum tube rays that the results 
have proven to be about the same. You will remember when 
radium was first discovered by those two great French chemists, 
Monsieur and Madame Curie, how all the newspapers and the 
medical and scientific journals took up and exploited the won- 
derful new element, 'Radium.' To-day we do not see quite so 
much about radium in the scientific journals and practically 
nothing in the newspapers. Does that mean that radium has 
lost its power, or to what do we attribute this falling off in 
the use of radium? The reason is this: It was found exceed- 
ingly difficult to extract the pure bromides of radium from the 
ore, the process requiring a long time and a great amount of 
work which, therefore, made the cost of pure radium enor- 
mously high. We have not one pound of pure metallic radium 
in the world to-day, and if we had, it is estimated that it 
would cost just about $33,000,000. With a small vacuum 
electrode that can be purchased for about $1.50 we can generate 
bi-ultra violet rays of equal power and volume to those emanat- 
ing from ten pounds of radium. That is the explanation ! 

There are certain cases, however, where the rays given off 
by radium can be used where we cannot use the vacuum rays, 
principally in the treatment of cavity conditions. For example, 
in the treatment of a case of cancer of the stomach, we take a 
small vial of radium, place it in a stomach tube and lower it 
directly into the stomach in close proximity to the diseased 
lesion. This you cannot do with a vacuum electrode. Radium 
has no application to dentistry to-day, although at one time 
its use was advocated by two Holland dentists who thought that 
its analgesic powers could be utilized in the treatment of 
pulpitis by the placing of a tiny vial in the root canal of an 
aching tooth. The dental profession, however, did not take up 
the idea and preferred the inexpensive use of arsenic or 
'pressure-anesthesia' and the removal of the offending pulp and 
filling the canal. 



30 



NOTES 



31 



NOTES 



32 



CHAPTER V. 

Tri-ultra Violet Rays, Their Nature, Characteristics, and How 

Generated in a Vacuum Tube 

The wave-length of the tri-ultra violet ray is .014 of a 
micron. It is situated at the very lower end of the spectrum 
and, being the shortest wave length of the three rays, it has, 
therefore, according to the law of penetration, the greatest 
penetrative power. It will penetrate all substances — even gold, 
platinum and silver — the densest metals, in thin sheets. The 
therapeutic properties of the tri-ultra violet or the X Ray are 
very marked; one of its principal effects being its analgesic 
power. We frequently find that in the short exposure necessary 
for the taking of a radiograph the pain from an acute attack 
of neuralgia of the fifth nerve, or from an ulcerated tooth is 
quite relieved, and its effects sometime seem almost magical. 
Nevertheless, it is a most dangerous method to use for the 
relief of pain, and should never be resorted to, particularly by 
the dentist, as there is always the temptation to repeat the 
dose too often at the urgent request of the patient, and conse- 
quently to produce conditions that are very hard to heal. How- 
ever, these conditions we will take up in a subsequent chapter. 

The X Ray is used in many cases of cancer with very good 
results, and where the cancer is superficial we have very often 
been able to attain a cure. If the cases are those of deep- 
seated tumors it is more difficult to get good results, inasmuch 
as we have to penetrate healthy tissue to get at the cancerous 
lesion. Cancers of the skin, therefore, can be said to yield 
very readily to X Ray treatment. Those situated near the 
surface, as for instance, cancers of the breast, are more diffi- 
cult, but very good results have been obtained, particularly 
if we can operate first. The modern technique in the treatment 

33 



of cancer is to operate first, wherever possible, and immediately 
after an operation to follow up with a series of X Ray treat- 
ments, even through the dressings. This, in most cases, prevents 
recurrence. There are many skin diseases that yield more or 
less to X Ray radiation, among which many be mentioned lupus 
vulgaris; lupus erythematosus; carcinoma, external, scirrhus 
and epithelioma; sarcoma; enlarged glands, scrofulous or other- 
wise; goitre, simple and exophthalmic; sycosis and favus; mol- 
luscum contagiosum; phthisis, pulmonary and laryngeal; rodent 
ulcer; hypertrichosis; pruritus; eczema; acne; warts, etc., etc. 

Let us now see how we can obtain these three rays. We 
will refer to Figure 2, which represents the interior of a large 
X Ray tube. 

We will suppose that we have a sphere of glass from which 
most of the air is exhausted, consequently there exists a state 
of partial vacuum. Vacuums are referred to as "high," 
"medium" and "low," a complete vacuum being impossible to 
attain. A high vacuum is where only one millionth part of the 
original air remains ; or an equivalent pressure of about .0003 
millimeters of mercury, while a medium vacuum would have one 
hundred thousandth part of the original air, and a low vacuum 
would be where one thousandth part remains, or an equivalent 
pressure of about .005 millimeters of mercury. 

In this sphere of glass (A) or X Ray tube, as we will 
call it, we have the condition of medium vacuum, i. e.. a 
hundred thousandth per cent, vacuum, which is about the 
degree of exhaustion necessary for satisfactory dental work. 
In this tube we have two metal electrodes represented in the 
diagram by the lines DWE and FXG. They are disks of metal 
placed at opposite sides of this tube and parallel with each 
other. They are connected by wires passing through the glass 
wall, to terminals on the outside, C and B. which can in turn 
be connected with the source of electricity. We will now pass 
a high potential current of electricity through this tube, i. e., a 
current of from 60,000 to 180,000 volts. This high potential 
current, the nature of which we will take up a little later, enters 

34 




Figure 2 — (see page 34) 




35 



at the cathode or the negative side, marked in the diagram by 
the minus sign, passes through the tube across the vacuum 
gap and impinges upon the anode or positive electrode marked 
by the positive or plus sign. The velocity of the electric 
current through a low vacuum has been estimated to be about 
124 miles per second. The current leaves the cathode disk 
(DWE) in the form of an invisible spark or electrical dis- 
charge. As we have said, wherever an electrical spark takes 
place ultra violet rays are produced; therefore, ultra violet rays 
are spontaneously produced all over the surface of this cathode 
disk. These rays take the path of the current; they travel 
through the tube with the same velocity (about 128 miles per 
second in a medium vacuum), in parallel lines, as indicated 
by the dotted lines in the diagram, until they strike upon the 
anode FXG, at the positive side of the tube. 

The enormous velocity under which these rays travel causes 
a shortening of the wave length. This may be illustrated by a 
simple simile. Take a long coil of rope and fasten one end 
to a post, and stand off some distance with the other end of 
the rope in your hand; very slowly shake the end up and down, 
and you will start a series of large waves, or a wave motion, in 
this rope. If you increase the velocity with which you shake 
this rope up and down, your waves will become shorter. This 
is analogous to what takes place in the vacuum tube. The great 
velocity under which these rays travel causes the wave-length 
of .21 of a micron to be reduced to about .1 of a micron. The 
ultra violet rays, therefore, lose their individuality and take on 
the characteristics of the bi-ultra violet ray, which has a wave- 
length of about .1 of a micron. Just where this transformation 
takes place we do not know. It may be close to the cathode or 
it may be close to the anode, or it may be just half way 
between; it makes no difference as to the ultimate result. The 
bi-ultra violet rays, when once formed by the breaking up of the 
ultra violet into the shorter wave-length, continue until they at 
last strike upon the metallic surface of the anode. Here they 
undergo their second transformation. The original ultra violet 

36 



rays had been reduced in wave-length to as great an extent as 
possible, by the velocity alone under which they were traveling. 
Now add to that velocity the sudden force of impact against 
the solid anode and we get a still greater reduction in the 
wave-length. The bi-ultra violet rays are shattered. The wave- 
length decreases from .1 of a micron to about .014 of a micron; 
or, in other words, the bi-ultra violet ray is transformed into 
tri-ultra violet, or the X Ray. The greater the velocity with 
which these rays travel the greater will be the impact against 
the anode, and the shorter will be the wave-length resulting 
from the impact. 

If the tube was actually constructed with the electrodes 
as represented by the lines DWE and FXG, in Figure 2, we 
would not, in all probability, get the double shortening of the 
wave-length. The bi-ultra violet rays would not be reduced to 
a wave-length as .014 of a micron, because, when they strike 
upon the anode, they would be reflected directly back upon the 
approaching rays, and would tend to retard these rays, conse- 
quently their force of impact would be considerably reduced. 
The reflected ray would not have as short a wave-length as it 
would if the approaching rays were not retarded. 

To remedy this effect we change the position of the anode 
and swing it to an angle of 45 degrees with the vertical. The 
line FXG now becomes the line HXK. As the rays strike 
upon this surface they are reflected downward, and consequently 
will not tend to retard the approaching rays. Still it would 
be nearly impossible to obtain an X Ray picture from such a 
tube. The reason for this is that the rays emanate from a 
series of points upon the anode, instead of one single point. 
If the area of the surface of the cathode disk were one square 
inch we could readily conceive of one million points of electrical 
discharge from this disk. Each point of discharge would 
generate its own ultra violet ray. We would then have 
one million parallel 'beams' of ultra violet ray traversing the 
tube, and they would consequently strike upon the anode in 
one million points. From each point X Rays would be gener- 

37 



ated and we would therefore have X Rays emanating from one 
million points. You will readily see that a tube of that kind 
would be useless to take a radiograph with, since an X Ray pic- 
ture is essentially a shadowgraph, and in this case there would 
be no sharp or distinct shadows. If you were to stand ten can- 
dles in a row in front of a screen, and then place your hand 
between the ten candles and the screen, there would be ten 
shadows of your hand thrown upon the screen, none of which 
would be very sharp. They would all be blurred and hazy; but 
if we were to merge all these ten candles into one candle of 
ten candlepower, we would have as a resulting shadow only 
one outline of the hand with ten times the intensity of shadow, 
but sharp and well defined. To accomplish this result in the X Ray 
tube we must bring these beams of approaching bi-ultra violet 
rays to a point, and that point must be upon the surf ace of the 
anode. We must therefore change the shape of the cathode 
disk. Instead of a straight disk, as shown in Figure 2, by the 
line DWE, we give to it the form of a concave mirror shown 
by the line DNE, and we place it at such a distance from 
the anode as to bring its principal focus directly to a point upon 
its surface. 

This is one of the most essential principles in the con- 
struction of an X Ray tube. The tendency on the part of 
many manufacturers is to get an imperfect or 'coarse focus,' 
with the result that X Rays emanate from a series of points, 
instead of from one single point. Pictures made with tubes of 
this character are not as clear as they would be if the tube had 
a 'pin-point' focus. In purchasing a tube, when the manufac- 
turer 'tries it out' for you, as he generally will, you should 
notice whether the point of light upon the surface of the anode 
is a 'pin point' or whether it is one-eighth or even one-quarter 
of an inch in diameter, as we sometimes find, and reject tubes 
where the focus is not sharp. 



38 



NOTES 



39 



NOTES 



40 



NOTES 



41 



SECTIONAL DIAGRAM OF X RAY TUBE 




Figure 3 — (see page 43) 



42 



CHAPTER VI. 
The X Ray Tube 

Figure 3 represents a sectional diagram of a modern X Ray 
tube. We note that the sphere of glass has two elongations at 
either end through which the electrodes FB and EA pass. 
These elongations separate the external connections for the high 
potential current, making a greater air gap for the current to 
jump than if the external connectors were on wall of the 
sphere itself as in Figure 2. This arrangement forces the 
current to pass through the resistance of the vacuum rather 
than overcome the greater air resistance from A to B on the 
outside of the tube. A plane, KL, passing through the 
tube and coinciding with the surface of the anode, divides the 
tube approximately into two hemispheres; the lower hemisphere 
ONP is called the hemisphere of activity, and the upper one, 
VM W, the hemisphere of non-activity. Anything placed on the 
lower side of the plane, KL, would be subjected to the 
radiation of the X Rays, anything placed on the other side of 
the plane, KL, would receive no rays whatever. 

We note in looking at this diagram, Figure 3, the third 
electrode, CG, which is marked with the positive sign. We 
therefore infer that it must be an anode, and we note also that 
it is connected exteriorly by means of a wire to the main anode. 
The shape of the inside surface, G, is usually a flat disk. The 
purpose of this electrode is to act as a safety valve for the elec- 
trical current. It answers the same purpose to the tube as the 
safety valve does on the steam boiler of an engine. If we throw 
in too great a pressure of steam, the safety valve blows open 
and the surplus steam escapes, thereby preventing an explosion 
of the boiler. The same thing takes place in the tube. If we 
throw in too heavy an electrical discharge, so great that the 

43 



capacity of the main anode cannot carry it off, the secondary 
anode takes up this surplus electricity and conveys it out of 
the tube and joins it to the conducting wire, returning it to its 
circuit, consequently preventing the current from striking the 
glass wall of the tube and puncturing it. 

All tubes are not constructed with this secondary anode. 
If the capacity of the main anode is large enough to carry off 
the heaviest current that we can force through the tube, there 
is no need for this extra electrode which is known by several 
names. It has been called a secondary anode, an auxiliary 
anode, and an anti-cathode, but the term principally used is 
the bi-anode. 

The main anode of the tube is constructed of three metals : 
first a disk, which is generally made of an alloy of platinum 
and iridium, or even a tungsten button, to withstand the very 
intense heat of the electrical discharge, focused to a single 
point, together with the bombardment of the bi-ultra violet rays 
upon its surface. This heat is so intense that if we had but 
the disk of platinum alone it would be immediately melted. 
It is therefore necessary to construct it of platinum alloy of 
the highest fusing point, or else with a tungsten button set 
into a surface of copper or brass. We next back up this disk 
of alloy with a solid block, F, of copper or brass, the block 
in turn being mounted on a hollow iron core extending back 
into the narrow neck of the tube. The purpose of this iron 
core and solid block, back of the disk or 'target/ as it is very 
often called, is to conduct the heat away from the surface, and 
distribute it, thereby reducing the intensity upon the surface 
of the target. Figure 4 represents an illustration of the modern 
type of X Ray tube, made by the Macalaster, Wiggin Co., of 
Boston, Mass. 

Another thing you will observe while the current is passing 
through the vacuum is the green coloration in the tube. This 
green color is not, as many people suppose, the X Ray itself 
(which you will remember is invisible), but is due to the: 
fluorescence of the rarified gas remaining in the tube after 

45 



partial exhaustion. The coloration depends on two things: 
first, on the kind of gas, and second, the quantity of gas 
present. 

In the X Ray tube we have to deal only with one kind of 
gas, and that is the atmospheric air which it originally con- 
tained. Upon exhaustion we leave it in a rarified state, and 
therefore, in passing a current of high potential electricity 
through it, it gives off this peculiar glow or fluorescence. This 
fluorescence, or coloration of the gas in the tube, serves us as a 
guide or index to the degree of vacuum, or exhaustion, of the 
tube; in fact, we have no other means of determining the 
quantity of gas in the tube. Unfortunately there is no meter 
or gage that we can attach to the tube and take a direct reading 
of its state of vacuum. We have to rely on our experience 
in the judging of the coloration, assisted by the reading of 
the milliamperes passing, as to whether the tube has a proper 
degree of vacuum or not. We will consider the coloration of 
air at different degrees of rarifaction. We will start at very 
low vacuum and go up to very high. A tube of very low 
vacuum is red, and as the vacuum increases the red changes 
to violet, the violet to blue, the blue to green, then through all 
the varied delicate shades of green, from very dark to very 
light, until at last we come to a bright canary yellow of highest 
vacuum. The entire range of efficient work in an X Ray tube 
used for dental work may be classified under the different 
shades of green, from dark to light olive. Experience only 
will determine the correct shade of green for the taking of a 
proper picture of the part in question. The degree of vacuum 
of a tube means a great deal to the operator, because it governs 
the amount of penetration of the X Rays; the higher the 
degree of vacuum the more penetrating will the rays be, and 
the velocity with which the rays and electrical current traverse 
the vacuum will be greater. The rays are therefore broken into 
shorter wave-lengths, and under the law of penetration the 
shorter the wave-length the greater the penetration; the con- 
verse is true in low vacuum. In low vacuum tubes we have 

46 



a greater volume of rays, and therefore a better or more 
brilliant coloration than in the higher degrees of vacuum, 
because the resistance of the vacuum is not as great to the 
electrical current, and consequently more current passes through 
the tube and more rays are generated, but they lack the 
intensity because they do not travel with a speed sufficiently 
rapid to cause a breaking up into the shortest wave-lengths. 
In the higher vacuum tubes, as the resistance increases to 
the electrical discharge, some of the current, instead of passing 
through the tube, jumps around the outside as a static discharge. 
In that case we only utilize part of the current, and therefore 
have a reduced volume of rays, but those rays travel with a 
greater velocity and generate more penetrating X Rays. A 
strange thing about all X Ray tubes is that, in an absolutely 
closed and hermetically sealed tube, the quantity of gas varies. 
This apparently paradoxical phenomenon can be explained by 
the fact that all substances are porous; porosity being one of 
the general properties of matter, and in the pores, or between 
the interstices of all matter, we have in most cases air. So in 
the metal parts, and even in the glass itself, of this tube, we 
have particles or molecules of air that have been held between 
the pores or interstices. Another principle of physics is that 
when bodies are heated they expand, and in the expansion 
they drive off the confined air. When we pass a current of 
electricity through the tube one of the first phenomena that 
occurs is the generating of heat in the metallic parts of the 
tube by resistance to the electrical current. Electrical energy is 
transformed into heat energy. The heat thus transformed 
causes the metals and the glass itself to expand. The air that was 
confined in them is therefore driven off and added to the supply 
already present in the tube, and consequently lowers the degree 
of vacuum. When the tube is allowed to cool again the gases 
are once more absorbed by the metals and by the glass that 
gave them off, but strange to say, a little more gas is absorbed 
than was originally given out. Just what causes this is not 
known, but the fact remains, and consequently we find that 

47 



the more we use a tube the higher "vacuum it will become. Each 
time we pass an electrical current through the tube we will 
probably note that it is a little bit- higher in vacuum than it 
was the time before. 

Since the vacuum has a tendency to rise with use, it 
becomes necessary to have some means of lowering it at will. 
The attachment on the tube, used for this purpose, is illustrated 
by D in Figure 3. It is called the regenerator or regulator. 

A small elongation projecting from the top of the hemi- 
sphere of non-activity is packed with a small wad of asbestos. 
There is a piece of platinum wire passing into the elongation 
connected with the exterior cap or terminal. To operate, we 
shunt the reduced electrical current from the cathode side into 
the regulator, either by a direction connection from the coil, or 
by causing the current to jump from the external cathode 
terminal A to an adjustable wire H, attached to the exterior 
regulator terminal, which latter is brought near to the cathode 
terminal when we wish to allow some current to be shunted 
through it. The current passing through the asbestos generates 
heat by resistance, which in turn causes the asbestos to expand 
and liberate the confined air, as there are many molecules of 
air held entangled in the porous asbestos. This confined air 
is driven off into the tube and so lowers the vacuum. 

This is a very desirable form of regulator, inasmuch as 
we utilize it with the current passing through the tube and 
we can therefore proceed intelligently, having the coloration 
in the tube as a guide to the extent to which to lower it. 
When we reach the proper shade we disconnect the wire that 
is carrying the current to the regulator, or bend up the wire- 
attached to the regulator terminal so that the shunted current 
no longer jumps its gap, and allow it to pass only from the 
main cathode. 



43 



NOTES 



49 



50 



NOTES 



51 



NOTES 



52 



Figure 5 



Figure 6 




Figure 7 




CHAPTER VII. 
Symptoms of High and Low Vacuum — Remedies for Same 

We will now consider the symptom's of low vacuum and 
symptoms of high vacuum, and the remedies for these defects. 
We will first suppose that the tube is working properly, with 
just the right- shade of green to give us a good dental 
radiograph (Figure 5). We will allow a heavy electrical 
current to pass through the tube and heat up the metal parts 
so that some gas will be driven off, causing the vacuum to 
drop a little. How can we tell when the vacuum is dropping? 
What is the first change we notice ? It is this : we note first 
of all a little puff of blue light right in front of the concave 
surface of the cathode. If we continue to lower the tube this 
blue puff of light, which resembles very much a little puff of 
smoke, gradually expands in the form of a cone, the apex of 
which extends toward the surface of the anode (Figure 6). 
If we lower it still more this blue light will at length bridge 
the gap between the cathode and the anode. The tube is then 
too low for a radiograph. When we first note the blue light 
we could still continue to take a radiograph, but it is a danger 
signal that the vacuum is going down. 

The first thing, therefore, that we have to look out for is 
the appearance of blue light in the tube, and when we see any 
indication of it we know that the vacuum of the tube is getting 
low. We must be careful not to allow the vacuum to become 
Too low, for if we do it will be nearly impossible to raise 
it again. By the time that the blue light reaches entirely across 
the tube it will be out of commission, as far as a radiograph 
is concerned. Let us suppose, nevertheless, that we continue 
to lower the tube or, rather, let us suppose that the tube has 
become punctured, the glass wall cracked, and therefore the 

53 



air from the outside is gradually forcing its way into the 
tube. We will follow the changes that take place in the tube 
until the air on the outside and the air on the inside have 
reached equal degrees of pressure. From the time when the 
blue light reached from cathode to anode we find that it will 
then extend and spread until the entire tube becomes of an 
even bluish color. Next we will note a little puff of pink 
light at the surface of the cathode, getting denser all the time 
in color until it finally becomes a decided red, and this red 
also takes the form or the path of a cone and travels from 
the cathode to the anode. It will then expand until the tube 
takes on a red coloration which indicates that the vacuum is 
very, very low. The next change we note is that this red coloration 
gradually fades away until we see absolutely no color in the 
tube, but instead there is a visible spark jumping from cathode 
to anode. When we see this we know that the vacuum in the 
tube has entirely gone, and there is the same pressure of air 
inside the tube as outside. 

Let us now consider the symptoms of high vacuum. Again, 
suppose the tube to be working properly, with just the right 
shade of olive green. What will be the first sign that the 
vacuum is increasing? First the shade of green will become 
lighter and lighter with an ever-increasing tendency toward 
yellow. Then we will note little dancing bright yellow spots 
of light throughout the tube, not confined to any place, but 
moving around (Figure 7). At first there will be just a few 
small spots, but as the vacuum increases the spots get larger, 
and they multiply in numbers until we have large yellow circles 
traversing the tube. We know then that the tube is very high 
in vacuum. We can also hear a crackling noise, caused by the 
static discharge. The current is not all passing through the 
tube as it should, since the vacuum of the tube has become 
too great for all the current to pass through; therefore, some 
of the current passes on the outside and follows the glass wall 
of the tube. When these yellow circles of light appear in the 
tube, it is time for us to lower the vacuum. If when we 

54 



first place the tube in commission, after it has rested, and we 
note the yellow spots the instant we turn on the current, do 
not lower the vacuum at once, but let it run for a few seconds 
and see if the metals, on being heated, and giving off gas, will 
not lower the vacuum sufficiently. If this is not the case, we can 
then resort to our regulator to lower the vacuum. Sometimes 
when putting on a new tube, or one that has been used a great 
deal, and has had a rest, we may find that the vacuum is so 
high that the electrical current will not pass through it at all, 
but instead jumps across the terminals of the coil, in which 
case it should be lowered at once by the regulator. The degree 
of vacuum is often referred to, as governed by the number of 
inches of spark it will 'back up' on the coil. To test this, 
start the tube with the terminal gap wide open on the coil ; now 
gradually bring the terminals together till the current starts to 
jump from one to the other, instead of passing through the 
tube. Measure this gap in inches. 

When an X Ray tube has become too low there is nothing 
that we can do to bring it up, except to allow a very small 
current of electricity to pass through it ; in the opposite direc- 
tion, so that we barely see a glow in the tube. Let it run this 
way for some time, and if during that time the vacuum does 
not come up we know the case is hopeless, and our only remedy 
is to send it to the manufacturer, who will re-exhaust it. He 
will break the 'seal-off,' through which the gas was originally 
pumped out, and will let the air into the interior, and again 
pump it out to the right degree of vacuum. This is an expensive 
process and it is better to prevent the tube from running too 
low, by careful watching, and avoid the re-exhausting of the 
tube. 

The remedy for high vacuum is simple, but we must be 
careful not to lower it too much. A tube of high vacuum has 
a smaller volume of rays than one of low vacuum, but the rays 
are more intense, because we have a higher potential current 
forcing its way through the high vacuum. The volume of rays 
being reduced in quantity, and the intensity being greater, 

55 



therefore the velocity with which the rays travel will be greater. 
Again, the velocity being greater than 124 miles per- second, the 
bi-ultra violet rays will strike the platinum anode- with an 
increased force of impact. The result is that the X Rays will 
be broken into still shorter wave-lengths, and by referring to 
the law of penetration, the shorter the wave length the greater 
the penetration; therefore, we have, from a very high vacuum 
tube, more penetrative power, although reduced in volume or 
quantity. 

In low vacuum tubes the entire current passes' through it 
and there is an increased volume of rays, but the intensity is 
not as great because the rays travel with a lesser velocity, and 
the rays have less penetration. 

The following table of comparative properties of high and 
low vacuum tubes should be carefully studied, as a thorough 
familiarity with these properties is most essential to the 
radiologist. 



56 



COMPARATIVE TABLE OF HIGH AND LOW 
VACUUMS 



HIGH VACUUM TUBES 
(Sometimes called 'hard' 
tubes.) 

Electrical discharge or 
'static' on outside of tube. 

Coloration tending toward 
3^ellow, with bright yel- 
low in places. (Remedy: 
lower vacuum with the 
regulator.) 

Less volume, or quantity of 
X Rays. 

More penetrating X Rays. 

Less contrast between 
blacks and whites, in 
radiograph. 

More exposure needed as 
compared with medium 
vacuum tubes, due to lack 
of volume of rays. 

Low milliamperage i n 
secondary circuit. 

Less danger of dermatologi- 
cal effects, due to greater 
penetration and less ab- 
sorption of X Rays by the 
superficial tissues. 

Glass wall of tubes more apt 
to puncture. 

Surface of anode less apt to 
burn out. 



LOW VACUUM TUBES 
(Sometimes called 'soft' 
tubes.) 

No electrical discharge or 
'static' on outside of tube. 

Coloration tending toward 
blue-green with blue 
puffs of light in places. 
(Remedy: give tube a 
rest, or reverse current on 
reduced potential.) 

Greater volume, or quantity 
of X Rays. 

Less penetrating X Rays. 

More contrast between 
blacks and whites in radio- 
graph. 

More exposure needed as 
compared with medium 
vacuum tubes, due to lack 
of penetration in X Rays. 

High milliamperage in sec- 
ondary circuit. 

More danger of dermatolo- 
gical effects, due to less 
penetration and more ab- 
sorption of X Rays by the 
superficial tissues. 

Glass wall of tubes less apt 
to puncture. 

Surface of anode more apt to 
burn out. 



57 



NOTES 



58 



CHAPTER VIII. 

The Essentials of an Outfit — Methods of Generating High Potential 
Electric Currents — Electrical Measurements 

There are four essential parts of an X Ray outfit for the 
dentist. First, the induction coil, or other means of obtaining 
our high potential current; second, the interrupter (providing 
an induction coil is used) ; third, the X Ray tube; and fourth, 
the X Ray 'tube-shield.' This last piece of apparatus is 
essential to the health and protection of the operator, and not 
to the working of the apparatus, but it is so important that 
we class it as one of the four essential parts of the outfit. 

There are four methods in general use for the generating 
of the high potential current; we will consider them in the 
order of their efficiency. 

First, the 'motor-generator-transformer' type, commonly 
known as the 'interrupterless,' with a maximum output of 
110,000 volts, and as high as 200 milliamperes. 

Secondly, the induction coil, with a maximum output of 
about 120,000 volts in a 12-inch coil, but with a milliamperage 
of from 15 to 30. 

Thirdly, the static machine, with a maximum output of 
about 200,000 volts in one of the largest machines, and about 
2^2 to 5 milliamperes. 

Lastly, the Tesla transformer, with an average maximum 
output of about 60,000 volts, and only 1 or 2 milliamperes. 

We will consider the types that we have mentioned, taking 
up first the most efficient, the 'interrupterless' type. This is 
an apparatus that represents the very latest achievement of the 
manufacturers. It is a type of apparatus that enables us to do 
instantaneous work in radiography. We will describe the con- 
struction of it very briefly. 

59 




Figure 8 — (see page 62) 
60 



If the direct current is the source of supply, then a rotary 
converter is used to produce an alternating current from the 
direct current. The motor set consists of a rotary converter on 
the direct lighting circuit, either 220 or 110 volts. The rotary 
converter changes the direct current into an alternating and 
passes it through the necessary switch, on the switchboard, and 
the rheostat to the transformer. On the end of the shaft of the 
motor is attached a round micanite disk. The low potential 
alternating current collected from the converter side is passed 
through the primary of the transformer which increases its 
potential to about 100,000 volts at a primary current of from 
25 to 50 amperes, depending on voltage used. The high poten- 
tial alternating current is then conducted from the transformer 
to a rotary polechanger, mounted on the armature shaft of 
the converter. 

The rotary polechanger consists of a round micanite disk.* 
To the periphery of this disk are fastened two copper strips, 
opposite each other, and occupying a little more than a quarter 
of the circumference. Parallel to this disk is a glass plate, on 
which are mounted four contact brushes equidistantly apart. 
They are arranged to commutate, or rectify the current 
from a high tension alternating, to a high tension, interrupted 
unidirectional current. The alternating current enters, as it 
were, at two opposite contacts, and the rectified current is 
taken from the two remaining contacts and conducted to the 
outlet terminals. 

The great efficiency and superiority of this type of appa- 
ratus lie not in its high potential, which is less than some of 
the larger types of coils, but is due to the great increase of 
current strength, or milliamperage, together with the fact that 
the current derived is unidirectional, thus cutting out all 
'inverse' in the tube. These outfits are very expensive and their 
use is adapted to the needs of the specialist who intends to take 
up general radiology as a profession, and practice it in all its 
varied fields and applications. To the specialist, therefore, the 
interrupterless type is not an extravagance, but is really a 

61 



necessity. Figure 8 represents the "King model" type of inter- 
rupterless outfit, manufactured by the Wappler Elec. Mfg. Co. 
of New York City. It is without doubt the "last word" in 
X Ray outfits. 

The next type of apparatus, the induction coil, is, on the 
whole, used more than any other type of apparatus. It is much 
less costly than the 'interrupterless' and fulfils the need of the 
average practitioner, in fact many specialists do all their work 
with a good-sized coil. In its latest form it is admirably .suited 
to the dental surgeon, and is more appropriate for his use than 
the larger and more expensive interrupterless kind. Figure 9 
illustrates the very latest type of X Ray coil, designed especially 
for dental work. With it, any dentist can well com- 

pete with the specialist and his interrupterless outfit. It is not 
only thoroughly efficient, but is much lower in cost than any 
other types of coil, and occupies the minimum of floor space 
in the dental office. It presents a truly scientific and aseptic- 
looking piece of apparatus. It is made by the American X Ray 
Equipment Co. of New York City. For the present we will 
pass over the description of the induction coil and consider the 
other two types. 

The third type of apparatus is the static machine, the use 
of which is becoming more obsolete every day. It is the only 
one of the four methods of generating the current for the 
X Ray tube in which the current is generated directly from 
friction and not stepped up from a low potential current as in 
the cases of the other three. In the static machine we have 
large wheels of glass revolving with metallic disks fastened to 
their surface at various intervals. These disks revolve against 
wire brushes and by means of the friction that is developed 
and the great speed with which they are revolving, generate 
frictional electricity. This electrical current is picked up and 
magnified by each revolution until it is delivered from con- 
densing leyden jars, to the terminals of the apparatus as a 
high potential static current. Small static machines are of 
very little value to the radiologist, and the larger ones are 

62 



The Standard 
Dental Outfit 
American X Ray 
Equipment Co. 




Figure 9 — (see page 62) 
63 




Figure 10 — (see page 65) 



64 



very expensive, even more expensive than the highest type of 
interrupterless apparatus and with an efficiency proportionately 
less. Figure 10 represents the latest and most improved model 
of static machine, made by Waite & Bartlett Co. of New 
York City. 

The last type, the Tesla transformer, is at the present 
time less efficient than the other three types, but it has one 
advantage of being the most portable, a complete Tesla coil 
that will generate a high potential current sufficient to taking a 
radiograph, can be carried readily in a dress-suit case and weighs 
only about twenty or thirty pounds. Such a piece of apparatus 
will give us a radiograph in from thirty seconds to a minute, a 
rather long time for the patient to remain still, but not impos- 
sible. It is less expensive than any of the others, and is to be 
recommended to those men who desire to get an outfit for as 
small amount of money that will enable them to do some X Ray 
work as an adjunct to their profession. It is a good starter 
for the man with the small purse and probably will be the 
forerunner of larger and more elaborate apparatus. 

A very complete and compact Tesla type of dental outfit is 
being placed on the market as this book goes to press, and 
from tests made with it bids fair to being a very efficient model 
of a low-priced outfit ; it is also made by the American X Ray 
Equipment Co. of New York City. 

We will now go back to the induction coil, its principles 
and construction, and methods of generating the high potential 
current. 

The current that we use in X Ray work is a high potential 
current, and by potential we mean electro-motive force or 
voltage. We must have a current of high voltage. If we 
attach our X Ray tube directly to the street current service 
wires, or to the wires from a battery we would have no result. 
The current would not pass through the tube. The reason for 
this is that the vacuum offers too great a resistance; to a low 
potential current the vacuum is an absolute non-conductor. 
Therefore a current that we can force through an X Ray tube 

65 



must be of at least 50,000 volts. Let us see how we generate 
this current in an induction coil. 

An induction coil consists of two principal parts, each one 
a separate coil of wire. The first coil has but a few turns of 
very coarse wire (for an X Ray coil it must be of 8, 10, 12 
or 14 gage wire), wrapped around a bundle of soft iron wire 
which forms the magnetic core of the coil. This first coil is 
called the 'primary' coil. The second coil is called the 'secondary' 
coil, and consists of a great many turns of very fine wire 
(usually number thirty-four silk-insulated wire is used in the 
secondary). 

Before taking up the physics of the induction coil let us 
first review some of the elementary principles of electricity, that 
we may have a clearer understanding of the operation of the 
coil. 

What is electricity? We do not know absolutely; we do 
know, however, that it is a form of energy that is invisible. 
At one time it was believed to be a liquid that was invisible, 
and that it permeated all substances, for the reason that its 
action followed so closely the laws of liquids. Therefore we 
very often use similes in hydrostatics (the laws of liquids at 
rest) and hydrodynamics (the laws of liquids in motion), to 
explain the phenomena occurring in electrical science. Even 
though the exact nature of this invisible force or form of 
energy, which we call electricity, is unknown, we are able to 
measure it. Instruments have been devised that will tell us just 
how much of this force, and to what extent it is being used. 
It .was necessary before we could do this, to originate certain 
units of measurement, just as we have units of measurement 
for weight, for time, and for volume. 

The first unit of measurement is the ( volt' which may be 
defined as the unit of electro-motive force. This tells us very 
little until we know what electro-motive force is, and to explain 
that we will consider a simple simile : — 

Suppose a tank of water is situated upon the roof of a 
tall building. From this tank of water we have a pipe leading 

66 



down to the ground floor, which can be tapped at all the inter- 
mediate floors to furnish the people in the house with water. 
At the ground floor there is a greater pressure than at the 
top floor; the tenants at the top of the house do not get as 
great a force of water as those living on the first floor, because 
of the weight of the water in the pipe, together with the laws 
of falling bodies, which materially adds to the pressure, or the 
head of water, at the lower level. This water pressure is 
analogous to voltage in an electrical current. 

The unit of measurement of electro-motive force means 
the unit of pressure. It is the amount of electricity measured 
in its potential, its power, its intensity or tension. In the case 
of the tank, the higher the tank is from the street the greater 
will be the potential, or the greater will be the force; and that 
force may be likened to the power that sets electricity in motion. 

Now suppose we have two pipes coming down from this 
tank, one a half inch in diameter and the other one two inches 
in diameter. Which will discharge the most water? The 
two-inch pipe you will say discharges more water. That is 
true, but it does not come with as great a force from the two- 
inch pipe as it does from the half-inch pipe. You have probably 
noticed that with a garden hose, if you press the nozzle to- 
gether, you can throw the water to a greater distance. You 
have increased the pressure. This pressure is analogous to 
voltage in an electrical current. 

The quantity of water passing through the pipe in a given 
time, that is, the number of gallons per hour, is analogous to 
the second unit of measure for electrical currents, called the 
'ampere.' The definition of the ampere is, the unit of current- 
strength; in other words, it is the amount of current passing 
a given point on a conductor in a given time. You see, there- 
fore, the difference between volts and amperes. The volt 
represents the intensity of the current, and the ampere repre- 
sents the rate of current-flow. One only exists at the expense 
of the other. Just as we have pressure and quantity in water, 
if we increase the pressure in the garden hose, we throw the 

67 



water a greater distance, but we do not deliver as much water 
in the same time. If we increase the diameter of the pipe and 
allow more water to pass it is not thrown to as great a 
distance; the pressure is less. One, therefore, exists at the 
expense of the other. 

The third unit of measurement that we have to consider, 
is the unit of resistance called the 'ohm.' It would be 
analogous in our water pipe to the number of curves and bends 
and to the friction of the water against the side. It is the 
resistance that the column of water has to meet with, and in 
electrical currents it is the resistance of a poor conductor 
which absorbs some of the electricity and converts it into 
another form of energy which we know as heat. If it were 
not for resistance we would have no incandescence in electric 
lamps. The ohm is the actual resistance offered to an electrical 
current by 150 feet of copper wire, one millimeter in diameter, 
or it is the resistance offered by a column of mercury one meter 
in height and with a diameter of one millimeter. 

We have considered the three practical units of electrical 
measurement, viz., the volt, the ampere and the ohm. The 
volt or the unit of electro-motive force, the ampere, the unit 
of current strength, and the ohm, the unit of resistance. One 
of the fundamental laws upon which all electrical science is 
based is known as Ohm's Law. The formula is this : 

C equals E divided by R. (C=— .) 

R 

In this formula C stands for current or amperes ; E stands 
for electro-motive force or volts ; R stands for resistance or 
ohms, so that we may write that same law in another way: 
Amperes equal volts divided by ohms. 

From this law, which is in the form of an equation, we 
can find any unit provided we have the other two units given ; 
for example, we will take a simple problem: How many 
amperes will pass through an electrical lamp operating under a 
potential of 110 volts and with a resistance of 220 ohms? 

68 



Applying the formula, it will read this way: X equals 110 
divided by 220. X being the amperes that we wish to find, 
110 representing the voltage passing through the lamp and 220 
representing the ohms of resistance to that current. Reducing 
this fraction to its lowest terms, we see that it equals y 2 ; 
therefore, we have ]/ 2 an ampere of current. By transposing 
Ohm's Law formula we have 

E=RXC, and R=tt- 



69 



NOTES 



70 



NOTES 



71 



Galvanometer 




Switch. 



Batter ij Cell. 



Figure 11 — (see page 73) 



72 



CHAPTER IX. 
Electrical Induction — Construction of X Ray Coils 

Let MN (in Figure 11) represent a straight wire connected 
at both ends with a battery, and let XY also represent another 
wire that is near to and parallel with the first wire, and con- 
nected at both ends to a galvanometer. We have, therefore, two 
separate and distinct circuits, the first made up of the wire 
MN, the battery B and. the switch S, which we will call the 
'primary' circuit. The other circuit consisting of the wire XY, 
which is of equal length and thickness as MN and the galvano- 
meter G, which will record the presence and comparative 
intensity of electrical impulses. 

We will now "make" the primary circuit, in other words, 
close the switch and allow a current of electricity to pass 
through the wire MN. At the instant that the current passes 
through the wire MN, a single impulse is generated in the 
secondary circuit, or the wire XY, which lasts but for a single 
instant, as shown by the deflection of the galvanometer needle, 
we will say, two points to the right and its immediate return to 
'O.' There is no more current passing through XY, although 
the current continues to pass through MN. When we "break" 
the current that is passing through MN (open the switch) and 
cause it to stop flowing, we will have another current generated 
in XY, but flowing in the opposite direction, as shown by the 
galvanometer needle deflecting two points to the left. This also 
will be but an instantaneous impulse and then it will stop. 
This phenomenon is known as induction and always takes place 
where we have a conductor in the neighborhood of another 
conductor, and when there is a current of electricity passing 
through the former. Induction takes place at its maximum, or 

73 



we say the inductiveness is at its maximum when the neighbor- 
ing conductor is parallel with the original conductor. If the 
neighboring conductor was at right angles to the one that the 
current was passing through, we would have no impulse, and 
it would vary^ from nothing to maximum as we swing the 
angle round through the quadrant of 90 degrees. The same 
phenomenon takes place in the induction coil. We pass a cur- 
rent of electricity through the primary coil and a current is 
induced in the secondary coil, the layers of which are parallel to 
each other. There is no connection between the two coils. They 
are both separate and distinct, yet a current is induced in the 
secondary coil when the current in the primary is started and 
when it is stopped. If the windings of the primary consisted 
of but. a single layer with a given number of turns and the 
windings of the secondary consisted also of but a single layer, 
with the same number of turns, the potential of the secondary 
would be the same as the primary, the voltage would not be 
increased, but if we increase the number of turns in the 
secondary we get an increase of potential which is caused by 
the phenomenon of self-induction; in other words, each turn 
of the secondary induces a current in the turn directly adjacent 
which must be added to the induction that is caused from the 
primary current, so that in the first layer of the secondary, if 
it had ten times the number of turns, the potential would be 
ten times as high as the primary; in the next layer it is the 
same as the first layer, plus the extra induction of the current 
flowing through the additional number of turns in the second 
layer of the secondary; in the third layer it is still higher, 
because the effects of the first two layers are added to the effect 
of the primary, and so on, through all the layers of the 
secondary coil. If we consider the number of layers and the 
number of turns that the secondary wire takes in the length 
of about twenty-eight miles (which is about the length of the 
secondary of a 12-inch induction coil) you can readily see that 
we are adding an enormous quantity of potential to the original 
current flowing through the primary coil. 

74 



As the voltage was increasing the amperage was decreasing 
with an equal ratio. The wire was very fine in the secondary, 
offering great resistance to the passage of the electrical current; 
consequently the rate of flow or amperage must be decreased 
as the potential increases, so that the output from the secondary 
coil would be perhaps 120,000 volts and about ten one-thou- 
sandths of one ampere, or 10 milliamperes. If we compare the 
original current in the primary of 110 volts (and we will say 30 
amperes), we will see that nothing is changed in value, only 
the form of the current has been transformed. It is the same 
case as though you took a ten-dollar bill to the bank and 
exchanged it for ten one-dollar bills. We have no more value 
than we had before, but we have it in a different form, so 
that it can do a certain class of work which we wish it to 
perform, where the other one would not. We have not created 
any new energy. 

The following table shows six manipulations of the primary 
circuit that give us impulses in the secondary. Let us carefully 
examine the table. 

TABLE OF PRIMARY MANIPULATIONS GIVING 
SECONDARY EFFECTS 



SECONDARY EFFECTS 




INVERSE 




DIRECT 


— to + 




+ to - 



PRIMARY MANIPULATIONS 



—2 Make 

— 1 Approached 

Increase of potential. 




+2 Break. 

+ 1 Withdrawn. 

+4 Decrease of potential. 

Under the heading, 'secondary effects/ we will see the 
words inverse and direct; inverse meaning a current flowing 
from negative to positive, and direct, a current flowing from 
positive to negative. In the two columns below we will find the 
manipulations of the primary coil that give us these effects in 

75 



the secondary; in other words, the causes for these effects. 
There are six causes altogether, or six manipulations of the 
primary that give us effects in the secondary. The first two 
are 'make' and 'break.' We will find in the first column 'make' 
and in the next column 'break.' This means that if you 'make' 
the primary, or start the current flowing, you get a single 
impulse in the secondary which is 'inverse'. in direction. When 
you 'break' the primary you get a single impulse in the 
secondary that is 'direct' in direction. The next two manipula- 
tions of the primary are the 'approached' and 'withdrawn' 
currents. We see in the first column 'approached' and in the 
second column 'withdrawn.' In order to explain the meaning 
of the 'approached' and 'withdrawn' currents, we will have to 
suppose that we have a small induction coil, operating with a 
battery and not from the street current, and having a primary 
that is removable; that is, the primary coil may be drawn out 
from the core where it rests inside the secondary. We will 
'make' the current in the primary. We get a single impulse in 
the secondary and then there is no more current flowing. The 
secondary circuit for the time being is 'dead,' although the cur- 
rent continues to flow in the primary. Now if we take hold of 
the primary coil and suddenly pull it out from the core, where 
it rests in the secondary, we get an impulse in the secondary 
circuit just as though we 'broke' the primary current. Again 
quickly replacing the primary back into the secondary, we get 
another impulse which is 'inverse' in the secondary. The 
'approached' and 'withdrawn' currents are obtained, therefore, 
by altering the relative distances between the primary and the 
secondary coils, either approaching the primary to the secondary 
or the removing of the primary from the secondary. The next 
two ways of obtaining impulses in the secondary are by the 
'increase' and 'decrease of potential.' In the first column we 
find 'increase of potential,' and in the second column 'decrease 
of potential.' We mean by 'increase' and 'decrease of potential' 
the increasing of the voltage and the decreasing of the voltage 
of the primary circuit. Suppose, in the small induction coil 

76 




that we just referred to, that we had a switch by means of 
which we could throw in the current from six dry cells in 
addition to a battery of ten, which we had originally. We first 
'make' the current with the battery of ten dry cells. We get 
one impulse in the secondary at the 'make.' Now with the cur- 
rent still flowing in the primary with a potential of 10 volts 
(each dry cell giving approximately 1 volt), we throw in, 
without breaking the circuit, an additional supply of voltage 
from the six extra dry batteries. We therefore have an 'increase of 
potential' in the primary circuit. The voltage is raised from 
10 to 16. At the instant that this takes place we have an 
impulse in the secondary which is 'inverse' in direction. Again, 
if we were suddenly to cut out six dry cells we would decrease 
this voltage from 16 to 10, and we would get an impulse which 
would be 'direct.' These are the six methods of obtaining 
impulses in the secondary, and they are the only ways by which 
we can get secondary impulses ; but they are not all equal to 
each other. 

Let us suppose that we have an induction coil without any 
internal resistance (which is impossible, although coils may be 
constructed coming pretty close to it), also let us suppose we 
have a sensitive galvanometer in the secondary circuit. We will 
'make' the primary, and show the impulse passing in the 
secondary by a deflection on the galvanometer. We will sup- 
pose that it deflects two points to the left. We will put down, 
therefore, opposite the word "make" the figure 2, and since 
it gives us the inverse discharge, we will mark it minus ( — ). 
When we 'break' the current we would get a deflection in the 
galvanometer of two points on the other side, provided, of 
course, the coil was without resistance; the needle having 
come back to zero would swing over to two points on the right 
side and register the single impulse and then comes back again 
to zero. We will put down opposite the word "break" this 
figure 2, with the plus (+) sign before it, because it represents 
a direct current flowing in the secondary. In the case of the 
approached and withdrawn current the galvanometer might 

77 



show only a deflection of one volt. We therefore put down the 
value, one, in both columns, with the minus ( — ) on one side 
and the plus ( + ) on the other. That means that the 
impulse of the 'approached' and the 'withdrawn' was only, 
in this case, one-half as great as the impulse of the 'make' and 
the 'break.' Now the impulse of the 'increase of potential' and 'de- 
crease of potential' may be twice as great as the 'make' and the 
'break,' depending on the amount of 'increase' and 'decrease;' 
therefore, the galvanometer would show, we will say, in this case 
a deflection of four points to the left and to the right, according 
as we 'increase' and 'decrease the potential.' We will put down, 
therefore, a value of minus ( — ) 4 for the 'increase of potential' 
and a value of plus ( + ) 4 for the 'decrease of potential.' Now, 
therefore, we have in this case a ratio of 'one is to two is to 
four.' This ratio is not always constant, but depends on several 
controlling factors; neither de we ever, in practice, have the 
inverse impulses equal to the direct impulses. They are always 
greater. 

The current that we use in the X Ray tube, that is, the 
high potential secondary current, entered the tube at the 
negative or the cathode side; it passed through the tube and 
out again at the anode or the positive side of the tube. This 
was, consequently, what we term an 'inverse current' flowing 
from negative to positive. This 'inverse current' is obtained 
from the secondary of the induction coil at the 'break' of the 
'primary/ and yet by looking at the table we see that the 
'break' of the primary should give us a 'direct' current in the 
secondary. This apparent discrepancy takes place because we 
have two factors taking place at identically the same instant. 
At the instant that we get our 'break' in the primary, zee also 
get an 'increase of potential' (produced automatically in the 
interrupter, which we will consider later), both taking place 
absolutely simultaneously. We have, therefore, the effect of 
a plus value, which was that of the 'break,' and the effect of 
minus value, which was that of the 'increase of potential,' to 
be added. This latter value always exceeding the former, and 

78 



in the case of large X Ray coils and electrolytic interrupters 
the intensity of the 'increase of potential' effect is sometimes 
twenty or thirty times as great as the 'make' and 'break' effects. 
The result being a predominance of the effect of the 'increase 
of potential' over that of the 'break,' giving us as a result an 
increased potential current, 'inverse 3 in direction, at the instant 
of the 'break.' The 'increase of potential' had a greater effect 
on the secondary than the 'break,' but as they were opposite 
effects the stronger is going to predominate over the weaker. 

In the construction of an induction coil for X Ray work 
we must have a 'primary' that is removable from the 'second- 
ary.' This, because it may be necessary to make a repair on 
the 'primary,' due to the short circuiting of the current. It 
would be inconvenient to unwind a great many miles of wire in 
order to get at the 'primary' to make a repair, and it is there- 
fore easier to construct the coil originally so that the 'primary' 
may be removed. Another requisite of a good coil for X Ray 
work is a thoroughly insulated 'secondary.' This is obtained by 
winding the secondary coil in two or more segments. The 
segments are insulated from each other and all boiled separately 
in a composition wax. Afterward, when they are placed in 
the case that will enclose them, and their terminals joined, the 
entire case, which is to form the finished coil, is filled with the 
same melted wax composite. This is the best form of insula- 
tion. If a current should jump from one layer to the other in 
the 'secondary,' caused by a 'breakdown' of the silk insulation, 
the wax in contact would also be melted by the heat generated, 
the melted wax would flow over the bad part of the wire and 
would reinsulate it. These are the two principal features of the 
construction of the coil. 

An X Ray coil has no vibrating interrupter attached to 
it as part of the apparatus. In X Ray work the interrupter 
forms a separate and distinct piece of apparatus, the 'coil' itself 
consisting of nothing but the 'primary' and the 'secondary' 
coils, the core and the terminals. 



79 



NOTES 



NOTES 



81 



Electrolytic Interrupter. 




'WEYNELT" TYPE. 




OXYGEN HYDROGEN 
GAS. GAS. 



P 



Figure 12 — (see page 83) 



82 




CHAPTER X. 
The Interrupter — Tube Shields — Valve Tubes — Wiring Diagrams 

It is necessary in order to obtain a practically continuous 
current in the 'secondary' coil to have some means for auto- 
matically 'making' and 'breaking' the current in the 'primary/ 
We cannot do this with sufficient rapidity by means of the 
hand, so we have to utilize some automatic principle. The 
instrument, by means of which we obtain these interruptions, is 
called an 'interrupter* 

There are two classes of interrupters, mechanical and 
electrolytic. There are a great many forms of mechanical 
interrupters, the simplest of which is the ordinary vibrator that 
we see on most of the small medical coils and buzzer bells. 
Their operation all depend upon some mechanical principle, and 
as there are so many of them we have not the space to consider 
the subject in detail. We will pass on, therefore, to the descrip- 
tion of the electrolytic interrupter. 

There are several forms of electrolytic interrupters, 
although they all depend on nearly the same principle. We 
will describe, therefore, the 'Weynelt' type of electrolytic 
interrupters. The construction is as follows : We have a 
large battery jar L (Figure 12), which is nearly filled with a 
solution of sulphuric acid and water; one part of sulphuric 
acid to six parts of water. The purpose of the acid in this 
solution is only to make the water a better conductor; water in 
itself is not a good conductor of electricity, but when it is 
acidulated the conducting power is very much increased. Into 
this acid solution we introduce two electrodes, a positive and 
a negative. The positive has a large extent of surface, while 
the negative has a very small extent of surface. These are 
the two principal features of the apparatus. The one shown in 

83 



the illustration G represents the positive electrode as a loop 
of lead wire. The reason why we use the metal lead is 
because it will not be affected by the dilute sulphuric acid. 

The negative electrode EFI is more complicated. It con- 
sists first of the insulated portion E, which is a tube of hard 
rubber of vulcanite, from which projects a small porcelain 
tube F. Through this porcelain tube and hard rubber tube we 
pass a lead wire P with a platinum point I, the tip of which 
only extends below the porcelain tube. This is the only part 
of the negative electrode that is exposed to the action of the 
electrical current. By means of the set screw AC, at the top, 
we can raise or lower our lead wire with the platinum tip, so 
that a greater or smaller amount of the platinum extends below 
the porcelain tube. 

When we pass a current of electricity through a liquid that 
has two electrodes immersed in it, we have the phenomenon of 
electrolysis taking place. The water of the solution is decom- 
posed into its hydrogen and oxygen elements. Hydrogen gas, 
therefore, is formed all over the surface of the positive elec- 
trode, but these bubbles of gas, H, do not remain upon the 
positive electrode; they take the path of the current through 
the liquid and are deposited upon the negative electrode I. The 
oxygen bubbles, O, are formed on the surface of the negative 
and remain there because they cannot flow against the action 
of the current, the result of which is that we have an accumu- 
lation of the two gases, hydrogen and oxygen, at the negative 
electrode. In the case of the Weynelt Interrupter the positive 
electrode has a great extent of surface, while the negative 
electrode is confined to a very small platinum tip, which pro- 
jects below the porcelain tube, and the bubbles of hydrogen, 
which were formed all over the surface of the positive elec- 
trode, passed through the solution and were deposited around 
the tip of the platinum point, therefore mixing with the oxygen 
gas, in the proportions of two parts of hydrogen to one of 
oxygen. This film of gas completely surrounds the exposed tip 
of the negative electrode, and acts as a non-conductor to the 

84 



current. Since two things cannot occupy the same space at the 
same time, the solution and the gas cannot both be in contact 
with the negative point at the same instant. Therefore, when 
the gas is in contact the liquid is not; but the liquid was the 
conductor of the current; therefore, if the liquid is not in 
contact there is no current flowing. The circuit of the current 
is broken. An electrical current passing from a large extent 
of surface to a small extent of surface will generate heat by 
resistance. The tip of the negative electrode becomes so hot 
that it glows with a white heat, therefore, we construct the tip 
of that electrode of platinum, which metal has a high fusing 
point. The mixture of hydrogen and oxygen gases form an 
explosive compound. The heat developed in the negative elec- 
trode is sufficiently great to ignite this explosive mixture, and 
we have an explosion. The chemical result of the explosion is 
the formation of water, which once more mixes with the 
solution, which again comes in contact with the electrode. The 
current is once more established, causing the 'make' of the 
circuit. Immediately the bubbles will again form, producing 
another 'break,' followed in quick succession by the explosion 
which again 'makes' the current, and so on, with great rapidity. 

With the Weynelt Interrupter it is possible to obtain 
250 breaks per second, and this rate of interruption may be 
varied by the turning of the set screw at the top, which adjusts 
the amount of platinum point extending beyond the porcelain 
tube into the solution. The greater the quantity of platinum 
exposed, the longer it will take for the bubbles to form, and the 
longer it will take for the surface to become heated; therefore, 
the less frequent the interruptions. When we draw up the 
platinum point and allow a smaller extent to protrude, we 
increase the rate of interruptions. Almost all electrolytic inter- 
rupters are constructed on similar lines and depend practically 
on the same explanation for their operation. 

We have seen from this description how we obtain our 
make and break. Let us now consider how we get our increase 
of potential at the instant of the break, that we discussed under 



85 



the theory of the induction coil. Let us go back to our old 
simile of the tank of water on the roof. Suppose we have a 
pipe discharging water into the tank. We will also assume 
that we have another pipe leading out from the tank which has 
exactly the same diameter of opening. You will see, of course, 
that the water will remain a constant height in the tank. It 
flows out just as rapidly as it flows in. We will also place a 
stopcock on the lower pipe, or the one leading out from the 
tank. If we gradually turn this stopcock closed, what will 
result? The height of the water will rise in the tank, and the 
amount of water coming out will decrease, but the potential, 
or the strength of that current, will increase. What have we 
done? We have raised the head of pressure (analogous to 
voltage) and we have decreased the rate of flow (analogous 
to amperage). At the instant that the stopcock closes off the 
supply of water the pressure has reached its maximum potential. 
This principle is exactly what takes place in the interrupter. A 
bubble of gas forms on the platinum point; then another 
bubble; then another, and so on, one after another, each one 
reducing the surface of the electrode that is exposed to the 
action of the electrical current, just as though we were turning 
the stopcock closed in the tank. We finally reach a point where 
all the bubbles have formed that can cover the surface of the 
electrode, with the exception of the last one, which will close 
the circuit. The potential has increased bubble by bubble to 
this point as its maximum. As the last bubble forms which 
breaks the current, the potential of the current coming from 
the positive has reached its maximum. The 'break' and the 
maximum 'increase of potential' taking place at the same 
identical instant. 

We have described three of the four essential parts of the 
apparatus, namely, the X Ray tube, the Induction Coil and the 
Interrupter. The fourth is the X Ray Tube Shield. This last 
piece of apparatus is absolutely essential, not to the working of 
the apparatus, but to the protection of the operator. There are 
different means of protection. Some operators prefer to cover 

86 



their own persons with a substance that is opaque to the X Ray, 
as, for example, a suit of lead armor, thus protecting their 
body from exposure to the X Rays. This method is not a good 
one. You will readily appreciate the discomfort of the operator 
carrying about with him a heavy suit of lead, and you may rest 
assured that the instant that he is through with the taking of a 
picture and has turned his current off, he will immediately strip 
himself of his lead suit. He forgets that the secondary rays, 
that are given off by every object in the room that has absorbed 
the primary rays, are still active in the room* and he therefore 
submits himself to the secondary radiation, which in time may 
produce even more serious results than those of the primary 
radiations. Another method that is sometimes employed for 
the protection of the operator, is a large screen which is lined 
on one side with sheet lead or other substance, opaque to the 
X Ray. This screen having a window made of lead-glass at 
about the height of the operator's eyes. When his apparatus 
is in action he goes behind the screen, and observes the working 
of the tube by watching it through the lead-glass window. 
Again, when he turns off the current, he steps out boldly from 
behind the screen and walks up the tube, forgetting again the 
secondary rays. For dental work this method of protection, as 
well as the first, are not only inadequate, but they are really 
dangerous to use. The best method of protection is not the 
shielding of the patient or the operator directly, but to place a 
box lined with some material opaque to the X Ray, such as a 
lead-glass shield around the tube itself, thereby confining all 
rays, both primary and secondary, to the inside of this box or 
shield. This device is called a Tube Shield. They are made 
in many different forms, but their requisite is that they be 
absolutely opaque to the X Ray, and that they do not conduct 
an electrical current. You will see, therefore, that it is impos- 
sible to line this box with metallic lead, which would otherwise 
be the best substance that we could obtain, for the reason that 



* The author has made an actual radiograph with the secondary emanations 
from objects in the laboratory that have received direct X Ray exposure. 

87 




the electrical current instead of passing through the tube, which 
has a high resistance, would, in preference, jump to the metallic 
lead lining and would pass through that as the path of least 
resistance. There are several substances that have been used 
with more or less success in the linings of these shields, all of 
which are non-conductors of electricity. One of the best mix- 
tures is that of red oxide of lead, subnitrate of bismuth, a 
little glue and plaster of paris. This mixture, when soft, is 
laid in a layer of about a quarter of an inch thick all over the 
insides of the box and after it has set and hardened, is painted 
with a lead paint. The opacity of this substance for the X Ray 
is very great. There are other forms, such as rubber that has 
been impregnated with lead salts, that also serve as good protec- 
tion, but it is decidedly necessary for the operator before he 
starts work to secure for himself a shield that gives really good 
protection. An excellent shield is constructed of glass 
impregnated with lead salts, not affecting its transparency, but 
rendering it proof to all X Rays, except those more penetrating 
ones obtained from very high vacuum tubes. These rays, how- 
ever, have hardly any dermatological effects. The opacity may 
be tested by the placing of a film and an interposed coin, on the 
outside of the shield and operating the tube for a short time 
and then developing your film, thereby determining whether it 
received any exposure to the X Ray or not. If the shield is not 
safe a shadow of the coin will be seen on the negative. Of 
course the shield must have an opening through which the rays 
can escape and reach the patient. Tube shields are usually 
made with different size openings. If constructed of a material 
opaque to ordinary light, it is well to have a window of lead- 
glass, so that the working of the tube and its coloration may 
be observed by the operator. If one stands out of the path 
of the ray as it emerges from the opening in a really good 
shield, he is absolutely safe from all exposure to the ray, and 
when the current is turned off he may rest assured that what- 
ever ray was given off was confined to the tube shield, except 
the small amount that passed through the opening, most of 



which was absorbed by the patient and carried away to be 
given off later as secondary radiation outside his office. 

When an induction coil is used to generate the high 
potential current, the 'secondary' output is necessarily an alter- 
nating current, since the impulses of 'make' and 'break' are in 
opposite directions. As we use only the stronger 'break' cur- 
rent in the X Ray tube, the weaker current of 'make' must be 
cut out of the tube circuit. This can only be done by introduc- 
ing sufficient resistance in the 'secondary' circuit to prevent the 
weaker current of 'make' from passing, but allowing the 
stronger 'break' current to complete its circuit. 

In a low potential circuit we would use *a resistance coil 
or rheostat to attain this result, but currents of high voltage 
cannot be controlled by wire resistances ; therefore we must 
resort to the use of vacuum and air gaps to sufficiently check 
the high potential impulses of 'make.' 

The best method for preventing the 'make' current from 
passing through the X Ray tube is to employ another or 
auxiliary vacuum tube in the 'secondary' circuit. This tube 
is called a valve tube. It is constructed on the same principles 
as the main X Ray tube, but has a funnel-shaped anode made 
of aluminum, instead of the platinum disk of 45 degrees. This 
anode reflects the bi-ultra violet rays directly back upon the 
approaching rays, thus retarding them and reducing their force 
of impact against the anode. As the bi-ultra violet "rays do not 
impinge upon the anode with as great a force as they do in the 
X Ray tube, they are not transformed into tri-ultra violet. No 
X Rays being formed, therefore, in the valve tube, it is not 
necessary to inclose this tube in a shield. The vacuum of these 
tubes is lower than in the main tubes. 

Air gaps, called spark-gaps, are also employed in some 
circuits to further cut off the 'make' current from passing 
through the tube. They are often made adjustable. This 
objectionable current of 'make' in the X Ray tube is frequently 
referred to as "inverse current." 

89 



AN INDUCTION COIL INSTALLATION 



SECONDARY CIRCUIT. 

VALVE TUBE. MAIN TUBE 

+ + 




PRIMARY CIRCUIT 



Figure 13 — (see page 91) 



90 



Figure 13 represents a complete wiring diagram for an 
induction coil installation. We will first trace out the path of 
the 'primary' current indicated by the straight arrows. It 
comes from the 'cutout' on the commercial circuit supply wires 
as a direct current of 110 volts, and we will say about 30 
amperes. It enters the interrupter by its positive electrode of 
lead wire, passes through this, and flows through the primary 
coil of the induction coil as an interrupted current. In the 
diagram the 'primary' coil is represented by the short-waved 
line, P, shown as situated outside of the 'secondary.' It must 
be borne in mind that this is only a diagrammatic method of 
representing it. In reality, the 'primary' has two or more 
windings and fits snugly inside of the 'secondary.' From the 
'primary' coil the current flows through a rheostat, R, and the 
switch, B, and so back to the negative side of the service 
'cutout.' 

It is not absolutely necessary to include a rheostat, or 
adjustable 'resistance box' in the 'primary' circuit. We do not 
find that there is much necessity for the reducing of the 
primary potential in dental radiography, other than when regu- 
lating the vacuum of the tube. Therefore, in some of the best 
outfits for dental work, there is in place of the adjustable 
rheostat, a fixed resistance coil which can be introduced into 
the circuit by a special switch. 

The switch, B, is to turn on and off the primary circuit 
in making the exposure. This switch, the rheostat or fixed 
resistance coil, the primary coil, and the interrupter, are all in 
series with each other, consequently it makes no difference as 
to their relative arrangement. The grouping of them, as shown 
in the diagram, is purely arbitrary. 

In the 'secondary' circuit we will start with the current of 
'break,' which is indicated by the broken arrows. It leaves 
the negative side of the coil, and jumps across the adjustable 
spark-gap, if open, thence to the cathode terminal of the main 
tube. It passes through the tube, leaving by the anode, enters 
the anode of the valve tube, passes through this, out through 

91 



the cathode of the valve tube, across the second spark-gap, and 
so back to the coil terminal on the positive side. 

The 'make' current, if it could flow, would start out from 
the positive terminal of the coil, as represented in the diagram 
by the wavy arrows, would jump the spark-gap and enter the 
valve tube by the cathode terminal. Passing through this 
vacuum, it would enter the main tube and flow as far as the 
surface of the anode. Here it would meet with the second 
vacuum gap that must be overcome. The potential, being lower 
than that of the 'break' current, is not sufficient to break down 
this added resistance; consequently it should not flow at all. 
In practice, however, some 'make' or 'inverse' tube-current does 
complete the entire circuit, even the second spark-gap. The 
small amount, however, that does pass the resistances can do 
but little harm in the actual working of the tube and the 
resulting picture. The lower the vacuums of the two tubes the 
more apt the 'make' current is to pass. 



92 



NOTES 



93 



NOTES 



94 



CHAPTER XL 
The Film and Its Preparation 

Radiographs of the various parts of the body are made 
with especially prepared photographic plates, called "X Ray 
plates." In dental work, however, it becomes necessary to 
take pictures inside the oral cavity. Glass plates are not 
suitable for this class of work. We therefore employ small 
cut films that have been especially prepared for the purpose. 
These can be placed in the mouth and made to conform with 
the curvature of the palate. 

The basis of these films is celluloid in thin transparent 
sheets. The celluloid backing is then coated with an emulsion 
of gelatin, that has been sensitized with certain chemicals, 
principally the silver bromides. This renders the film sensitive 
to all actinic rays, and, of course, the operation of sensitizing 
must be carried on under the non-actinic light of a red lamp. 
The exact formula with which the films are sensitized remains 
a trade secret of the manufacturers. There have been many 
different makes of films advocated for dental radiography. 
Some are more rapid than others, but where the speed of the 
film is materially increased, the contrast or gradations in 
'lights and shadows' will not be so good. An ideal film, espe- 
cially prepared for dental radiography, consists of the 'Eastman 
Dental X Ray Film.' This film has been used with entire 
satisfaction by the author for the last ten years. It is not a 
particularly rapid film, requiring fairly long exposures, but 
where the element of time is not essential ; that is, where the 
type of apparatus is powerful enough to give good results in 
five to ten seconds' exposure, with these slower emulsion films, 
their use is certainly to be advocated. Recently the Eastman 
Company have been experimenting with several new emulsions, 

95 



to the end that they might increase the working speed. They 
have succeeded in turning out a film about five times as fast 
as their old ones. After repeated trials with the new films the 
author has gone back to the old ones, getting better grades of 
contrast with the slower emulsion. Another film that is used 
extensively is an English product, made by the Ilford Company 
of London. These films are made in several sizes and shapes. 
They are, by actual test, about ten times as fast as the 'old' 
Eastman film. Where great speed is required, as, for example, 
with some of the types of apparatus that give but a minimum 
potential, their use is to be strongly recommended. 

The standard size of the dental film is 1% x \y% inches. 
This is a good average size, and can conveniently be placed in 
the mouth. In cases of very small children, the size may be 
cut down by the operator. 

The 'old' Eastman film is supplied in small paper packets 
of standard size. There are two films placed in each packet, so 
that two duplicate radiographs are made by the single exposure. 
This is a most useful and desirable practice. The films are 
wrapped in black paper when received ; each packet being 
sealed by a white paster on the back, or non-sensitive film 
surface of the packet. The films are lightproof when received, 
but they are not moistureproof. They cannot be placed in the 
mouth as they are, as the saliva would penetrate the black 
paper and ruin the films inside. We must prepare these films 
before using, by wrapping them in thin sheets of palate rubber 
or other moistureproof material. The author uses an extra 
thin grade of palate rubber, made in two colors — the brown or 
pure rubber and red. The paper packets are laid sensitive side 
dozvn, upon the red rubber, the cloth covering being first 
stripped off one side of the rubber. A sheet of the pure rubber 
is then placed over the packet and allowed to overlap a little, 
the same as with the red. On pressing the edges tightly 
together, by running an instrument of some kind, or the finger 
nail, around the outline of the film packet, the two rubber 
surfaces will cohere perfectly. The surplus rubber is then 

96 






trimmed off, care being taken not to cut into the paper packet. 
The resulting packet is quite waterproof. 

Films should not, however, be wrapped in rubber for any 
length of time, as the sulphur in the rubber will work its way 
through the paper film covering and injure the films. It is 
not well to leave films so prepared longer than about twelve 
hours in the rubber covering. The 'new' Eastman film is 
furnished in an outer covering of red waxed paper. This is 
moistureproof in itself and needs no extra rubber wrapping. 
The Ilford films are wrapped in an outer coating of gutta- 
percha, which protects them from moisture. 

Some makes of dental films have rounded corners, so that 
when placed in the mouth the corners will not dig into the 
tissues. 

As a matter of fact, the number of cases where the sharp 
cornered film causes any real discomfort to the patient are 
very few, and the operator can, in those cases, go into his 
dark room, and with the light of his red lamp trim away the 
one offending corner, and rewrap the film. This is a better 
practice than rounding all the corners of all films, since we do 
not sacrifice any of the valuable film surface, which is really 
small enough as it is. 



97 



NOTES 









98 



CHAPTER XII. 
Application of the Principles of Shadows, to Avoid Distortion 

Before proceeding with the methods of placing the film in 
the mouth, we will first take up a few principles that have 
an important bearing on this part of the subject. 

"A dental radiograph might be defined as a shadow graphic 
representation of the several dental tissues, taken plane by 
plane, and each plane superimposed on the next, from facial 
to lingual surface." Note particularly that the radiograph is a 
'shadowgraphic' and not a 'photographic' representation of the 
tissues. The images that we see on a dental negative are not 
the actual teeth photographed on the film, but merely shadows 
of the actual teeth. Since, therefore, we deal only with 
shadows, you will readily appreciate how easily these shadows 
may be distorted. Wherever a shadow is cast, it must be of 
some object that is between the surface upon which the shadow 
is thrown, and a source of illumination. The source of illu- 
mination may be the sun, an arc lamp, or other light-producing 
medium, or it may be the radiations from an X Ray tube. The 
surface upon which the shadow is cast we will call the 'screen.' 
The relative positions of the object, the source of illumination, 
and the screen, determine the size of the resulting shadow. 
Shadows may be distorted by 'elongation' or by 'foreshortening.' 
The same laws apply to the shadows cast by the X Ray, as 
with any other source of illumination. 

The closer the object is to the screen the clearer and 
sharper will be the resulting shadow, and the more exact in 
size. Hold your hand between a lamp and a sheet of white 
paper, as a screen, at the distance of about a foot from it, 
and observe the shadow cast. 

99 



SHADOWS 



Fore-shortening 0$ Shadows. 





\ H - 



Fig.14 



Fig. 15. 



Fig. 16. 




Elongation Oj Shadows.- 



Fig.17 



100 



You will note first that it is very much enlarged, and 
secondly, the outline will be faint and indistinct. Now slowly 
approach the screen with your hand. You will observe that 
the shadow becomes more distinct and smaller, till at length, 
when the hand is almost touching the screen, the shadow will 
be good and black, and of almost the exact size of the actual 
hand. From this experiment, we learn that in radiography the 
closer we get the plate or film to the tissues we wish to show, 
the clearer and sharper will the resulting picture be. 

Let us refer to Figure 14, which represents a man standing 
on a sidewalk at night, with an arc lamp directly over his head. 
The arc lamp is represented by A. The direction of the rays 
of light by AD, and the shadow of the man cast upon the walk 
as BC. When the source of light is directly over the man the 
only shadow that is thrown at all is a small spot directly at 
his feet. Now suppose that the man takes a step forward and 
assumes the relative position with the arc lamp as shown in 
Figure 15. His shadow begins to take shape, but it is con- 
siderably shorter than the actual height of the man. If he 
now takes another step forward, as shown in Figure 16, the 
shadow will assume its correct length; that is, equal to the 
height of the man. Once more, suppose the man took another 
step forward, till the relative positions of the man and the lamp 
are as shown in Figure 17. The shadow is now much longer 
than the height of the man. It is an elongated shadow. If he 
were to continue to advance, the shadow would also continue 
to elongate, till, at length, when the lamp was directly behind 
the man the length of the shadow would be 'infinity.' We 
see, therefore, that, as the relative positions of the object and 
the source of illumination vary, so the length of the resulting 
shadow upon the screen varies from nothing to infinity. 

In the dental radiograph the shadows of the teeth upon 
the film would also vary from nothing to infinity, according as 
we changed the position of the X Ray tube. We must be able 
to determine just where to place the tube in order to get a 
resulting shadowgraph of the teeth with correct root-lengths. 

101 



Let us again refer to Figure 16 — the plane of the object will 
be represented by the line EDB, and the screen by the line BC. 
These two lines form, with each other, the angle EBC, which 
in this case is a right angle. If we bisect this angle we get 
the line FHB, and we note that the direction of the rays 
indicated by the line AHC is perpendicular to the bisecting 
plane at the point H. When this takes place the resulting 
shadow will be the same length as the object. 

From the above illustration we may formulate a rule for 
the directing of the rays of light to fall upon a given object, so 
as to get a correct shadow length upon a screen placed at an 
angle to the object. This rule may be expressed as follows: 
'Bisect the angle made by the plane of the object, and the plane 
of the screen, and direct the rays so that they will fall per- 
pendicular to this bisecting plane.' 

Let us see how this rule works out as applied to the 
taking of a radiograph of the teeth. Figure 18 represents a 
sectional diagram of a superior right bicuspid tooth situated in 
its socket in the alveolar process of the superior maxilla. T is 
the tooth, S represents the antrum or maxillary sinus, and 
D the film placed in the mouth and pressed up into the 
curvature of the palate. The line AB represents the plane of 
the teeth, and CB the mean or average plane of the curved 
film. Suppose we place the X Ray tube at X, and direct the 
rays, as shown by the arrow, perpendicular to the plane of the 
tooth. Will we get a correct shadow length of the roots of 
the tooth upon the film? We will plot out the projection of 
the tooth upon the film and see. Draw two lines from the 
tube X to either end of the film, as XY and XF. These lines 
intersect the tooth at M and X, therefore a shadow of that part 
of the tooth between the points M and X will be projected 
upon the film D, and will have the length of the dotted line 
EF. This line is much longer than the line MX. consequently 
we have, in this case, considerable elongation. The apex of 
the root will not be shown at all upon the film, since, if we 
draw a line from the tube X to the apex of the tooth's root 

102 



X-eS? 



;>v > s- > ^ 



Elongation 

X. Fig-18 




Correct Shadow Length. 



Fig.20. B 

(See pages 102 and 104) 



103 



and continue it to Z, we see that it does not touch the film 
at all. 

From this diagram we learn that in the superior arch we 
cannot direct the rays perpendicular to the plane of the teeth. 

Referring now to Figure 19, we will direct the rays per- 
pendicular to the mean plane of the film. In this case the 
projected shadow of the tooth EF is shorter than the actual 
tooth length, therefore we see that by directing the rays per- 
pendicular to the mean plane of the teeth we get foreshortening 
in the root lengths. We note, however, that in this diagram the 
line XY, representing the extreme upper limit of the field of the 
picture, passes through the antrum, and gives us a shadow of 
its lower half. 

In Figure 20 the line KB represents a plane bisecting the 
angle made by the plane of the teeth, AB, and the mean plane 
of the film, CB. If we direct the rays perpendicular to this 
bisecting plane, and at a point opposite the apices of the roots 
of the teeth, the resulting radiograph will give us approximately 
correct root-lengths, as shown by comparing the lengths of the 
lines EF and MN. Note carefully the relative positions of the 
X Ray tube, and the film, to obtain this result. Of course the 
position of the tube, as regards the exterior part of the face 
of the patient, will vary according as the patient has a high 
or a low palate. 

Suppose we had to obtain a radiograph of the maxillary 
sinus, we would raise the tube up still higher than as shown in 
Figure 19, and direct the rays downward, in a line just passing 
under the patient's eye. Of course the film should be placed 
higher across the palate, in which case only the apices of the 
roots of the teeth will show on the lower part of the negative. 



104 



NOTES 



105 



NOTES 



106 



CHAPTER XIII. 
Technique of Taking the Picture 

Before taking a dental radiograph the operator should 
ascertain, whenever possible, the 'suspected' condition of the 
patient that renders the radiograph desirable. Of course 
this is not always evident, but there are times when 
we wish to inspect a certain root-canal as to the extent that it 
has been filled, for example, or again, we may be looking for 
the presence and position of an unerupted tooth. In the first 
case we should take the picture so that the resulting shadows 
would be of the correct length. In the second case the actual 
root-lengths are not at all necessary to show; in fact, we should 
purposely foreshorten the shadows on the radiograph, so as to 
cover the area above the roots of the teeth, where the missing 
tooth is most likely to be. We should always endeavor to so 
direct the rays as to show with the maximum clearness the area 
that we believe to be involved. From this you will see that 
we do not, in every case, try for correct shadow lengths, but 
in many cases — in fact, we may say the majority of cases — we 
deliberately distort the shadow lengths for the purpose of 
covering a higher area. The only distortion, however, that we 
consider permissible is that of foreshortening. Under no con- 
ditions do we elongate the shadows. Pictures showing any such 
distortion are evidence of faulty technique. Foreshortening the 
shadows does not render them any the less clear, as does elonga- 
tion, but rather it tends to intensify the detail. In cases where 
we deliberately foreshorten the shadows we take this fact into 
consideration in the subsequent translation of the radiograph. 

Let us suppose that we are thoroughly equipped for the 
taking of dental radiographs, with an up-to-date outfit, we will 
say, a coil installation, and a patient presents with a history of 

107 



a fistulous tract in the region of the superior right bicuspids, 
discharging pus into the mouth. We presume that there is an 
abscess somewhere, we might attempt to locate it without 
resorting to the X Ray, but we would only be wasting the 
patient's time and our own as well. We turn, therefore, to a 
radiograph. Let us follow, step by step, the procedure in the 
taking of this radiograph. 

We first see that the patient is comfortably seated in the 
dental chair, or some other chair with a good head-rest. The 
head should be so adjusted that it is almost erect and securely 
placed in the head rest. We then proceed to the preparation 
of the film. Films and plates should be always kept in a lead- 
lined, X Ray proof box, or else in a room far removed from 
the operating room, otherwise they might be prematurely 
exposed, if the tube shield should be pointed in their direction. 
We take a film, therefore, from our lead-lined box and wrap it 
in palate rubber, unless it is one that has been already made 
waterproof. We are careful in wrapping it that we get the 
sensitive side of the film package against the red rubber. The 
film is then placed back in the box. 

We next examine carefully the patient's mouth and note 
whether the palate is high or low. If we are not experienced 
in the taking of these pictures we should proceed at this stage 
with deliberation and special care. We consider the area we 
wish to show. As it is a suspected abscess condition the 
direction in which it points is unknown. The antrum even 
may be involved. We wish to show as much of the area 
above the teeth as we can without sacrificing the roots 
themselves. 

We must, accordingly, foreshorten the shadows somewhat. 
We come to the conclusion that if we place the tube so that 
the rays are directed perpendicularly to the plane of the film 
we will include considerable area above the roots of the 
teeth, and will show even the floor of the antrum. (See 
Figure 19.) It is not as easy to direct the rays perpendicular 
to a given plane in practice as it is to plot it out on paper. 

108 



However, with a little practice, this will come by instinct. The 
experienced operator subconsciously places the tube in the posi- 
tion to best show the condition, depending on the height of the 
patient's palate. For this reason it is well, from the start, to 
note very carefully this height in each case, and to associate 
it in your mind with the position in which you place your tube. 
For the beginner, it is well to actually plot out on the patient's 
face imaginary lines that coincide with the planes of the teeth 
and the film, and even the bisecting plane. 

In nearly every case certain 'landmarks' will present which 
will serve as guides to these imaginary lines. For example, 
with the case we have assumed, let us suppose that the mean 
plane of the film in the mouth coincides with an imaginary line 
drawn on the patient's face from the right-hand corner of the 
mouth to the inner corner of the left eye. With this imaginary 
line in mind, move your tube shield till the direction of the 
rays, as they will come through the opening, will fall perpen- 
dicular to a plane passing through the face along the imaginary 
line. 

When you have the tube shield adjusted to the proper 
angle caution your patient not to move the head under any 
consideration, and then connect the wires to your tube shield. 
Be particular to see that the wire connected to the valve tube 
side of the coil leads to the anode of the main tube. When 
this is done tell your patient that you are going to turn on 
the current, and that there may be a slight noise of sparking, but 
not to 'jump' or change the position of the head. Now close 
the switch of your 'primary' circuit and allow the current to 
pass for about two or three seconds only. Note whether the 
current is passing through the tube in the right direction by 
observing if the hemispheres of activity and non-activity are 
well marked. Also note if the coloration is good, indicating 
the proper degree of vacuum, and that the current is not 
jumping to any nearby object. 

If all appears well in this flash-view, flash it again "to 
make assurance doubly sure." Then, still finding everything 

109 



all right, wash your hands thoroughly, procure the film that you 
have wrapped from its box and take off the cloth covering 
from both sides of the palate rubber, bend the package in 
your ringers several times to make it flexible, and insert the 
package in the patient's mouth, being careful to place the red 
or sensitive side toward the tube. Press this well into the 
curvature of the palate, being particular not to let the inside 
top corner come in contact with the soft palate if you can 
possibly avoid it. Now remove your fingers, first telling the 
patient to put the left (in this case) index finger on the film 
and to gently press it steadily against the side of the roof of 
the mouth. Once more look to the position of your tube and 
see if in placing the film in the mouth you upset the proper 
angle; if not, tell your patient that you are going to take the 
picture and to keep absolutely motionless. If your type of 
apparatus allows the taking of the picture in but a few seconds 
caution your patient, in addition, to take a long breath and 
hold it. 

Now, stop-watch in hand, or at least a watch with a 
second hand, close your switch sharply and make the expo- 
sure, timing it very carefully. During the exposure observe 
the appearance of the tube, whether the vacuum is lowering or 
not, the reading of your milliamperemeter, if you have one in 
the secondary circuit; and above all. watch your patient, and 
see if you observe any movement. If you do, stop the exposure 
and take another. 

When the exposure is complete, open your switch and 
remove the film from the patient's mouth. This done, strip the 
rubber from the film packet, write its number on the back, put 
it in an envelope with the name and other data on it and return 
the paper film packet to the lead-lined box. Disconnect the 
tube and move the shield away from the patient's chair. 

The above procedure should be followed as closely as 
possible in every case. Of course there will be circumstances 
that will alter each individual case, and they will have to be 
dealt with accordingly. 

110 



In radiographing the inferior molars and bicuspids the film 
will be about parallel to the plane of the teeth, and the rays 
can be directed perpendicular to it. In all other cases you will 
have to take into consideration the bisecting plane or the film 
plane. Try, wherever possible, to get the upper edge of the 
film flush with the morsal surfaces of the teeth in cases of the 
lower arch. 

In some cases you may have trouble getting the patient to 
hold the film in the mouth. NEVER, UNDER ANY CIR- 
CUMSTANCES, HOLD THE FILM IN THE MOUTH 
YOURSELF DURING THE EXPOSURE! This caution 
cannot be emphasized too strongly. The temptation is often 
great to hold the film in a difficult case, but don't do it! 
Your hand, in holding the film, receives as much exposure as 
the patient does, which in itself is negligible, but if you do it 
once you are apt to repeat it with other cases, and before you 
are aware of it you have exceeded the limit of safety and will 
develop a case of dermatitis. The effects of the X Ray are 
unfortunately accumulative, and an exposure of ten seconds to- 
day, twenty to-morrow and twenty next week, and even ten 
next month, would have the same effect as one minute exposure 
at one sitting. There are many of the early operators who 
have lost their fingers, hands, arms, and even their lives, as 
the result of exposure years ago, before the danger of the ray 
was known. It is not so much the direct effects (the der- 
matitis) that is so serious, but it is the X Ray cancers that 
develop on the seat of the old dermatitis years later. Be 
warned in time and you will find that there is no more danger 
in radiology as practiced to-day than in photography itself. 

In cases where you may have trouble in getting the patient 
to hold the film in the mouth, you may be able to get someone 
who, perhaps, is accompanying the patient, to do so. If this is 
impossible there is always one method that we can use, which 
we will consider when we come to the technique of stereoscopic 
dental radiography. 

Ill 



The distance of the tube from the face makes a good deal 
of difference in the time of exposure. The intensity of the 
X Ray, like any other form of light, varies inversely with the 
square of the distance from the object illuminated. It is not 
well to have the tube too close, because the shadow will be 
enlarged. In practice 18 to 24 inches will be about right. 
Whatever distance you adopt, with your outfit, keep this dis- 
tance constant in all your pictures. It is not advisable to have 
too many variable factors in your technique. The more constant 
we keep the conditions under which we work the better will 
be our results. 

The four most difficult radiographs to get in the mouth 
are the four third molars. The superior third molars, and 
even the second and first, are hard to get, because the inside 
top corner of the film packet is apt to come in contact with 
the soft palate and cause the patient to gag. When the patient 
once starts to gag there is little hope of getting the picture 
without anaesthetizing the palate. In placing the film in the 
mouth, in a superior molar case, be very careful not to push 
it too far back. In fact, it is better to place it in about the 
bicuspid region, and very slowly and carefully work it back 
till, at length, we get it far enough back to show the third 
molar area without having touched the soft palate at all. Also 
be careful in putting the film in, that the inside edge does not 
drop down and touch the back part of the tongue. If patients 
show any tendency to gag, caution them to take several long 
and deep breaths through the nose. If, in spite of these pre- 
cautions, they commence to gag, and they often will, there is 
only one thing to do, and that is to anaesthetize the palate. 
This is done by using a 5% solution (3% with children) of 
cocaine, and to spray it on the hard and soft palates until an 
atomizer. They should be told not to swallow any more of the 
solution than they can possibly help. In about five minutes 
after this operation you can proceed to the taking of the picture 
without any more trouble. 

112 



The inferior third molars are hard to get in many cases, 
because the corner of the film is apt to dig into the floor of 
the mouth under the tongue. The film should not be cut if 
you can possibly avoid doing so. In these cases we should 
remove the packet from the mouth, and taking the two rubber 
surfaces over the offending corner, between the thumb and 
forefinger of the right hand, and holding the rest of the packet 
securely with the other hand, pull out the rubber a little at the 
corner and then pat it back again. This should make a little 
pad or cushion over the sharp point of the film. Another 
method is to bend the corner back and so give it a rounded 
effect. Either of these methods is usually sufficient, but there 
are some cases, with a very small mouth, where it is. absolutely 
necessary to cut off the corner. This, of course, must be done 
in the dark room with the aid of the red lamp. The black 
rubber can then be pulled down over the cut and lapped over. 
However, if this is done the rubber must not be removed till 
you are ready to develop it in the dark room. And that should 
be as soon as possible after taking. Also the packet should 
not be exposed to any bright light, but should be shielded as 
much as possible by the hand. The safer method, though, if 
you have the time, is to unwrap the film in the dark room, cut 
the corner of the film itself, rewrap it in its black paper, 
turning over the corner of the paper where you have snipped 
off the film, and then rewrap the packet in palate rubber. 

In taking pictures of the inferior teeth always try to get 
the film down low enough to show the lower border of the 
inferior maxilla. This is not always possible, but if you proceed 
gently, but slowly and firmly, watching carefully for the 
wincing of the patient, you will be surprised in many cases 
how far down you are able to press the film. 

In pictures of the inferior centrals the patient's head should 
be dropped very far back in the head rest, and the tube shield 
placed over the chest. The rays should then be directed per- 
pendicular to the plane of the film. 



113 



Before leaving the subject of the technique of taking the 
picture, we will summarize the steps that should always be 
observed. It would be well for the beginner to commit this 
procedure to memory, rather than to hesitate in the presence 
of the patient. There is nothing so disquieting and less reassur- 
ing to the patient than signs of indecision on the part of the 
operator. 

In the taking of a dental radiograph always proceed as 
follows : 

FIRST. GET THE PATIENT COMFORTABLE. 

SECOND. PREPARE THE FILM IF YOU HAVE 
NOT ALREADY DONE SO. 

THIRD. EXAMINE CAREFULLY THE PATIENT'S 
MOUTH. 

FOURTH. ADJUST THE TUBE SHIELD TO 
DIRECT THE RAY PROPERLY. 

FIFTH. CAUTION THE PATIENT NOT TO MOVE 
THE HEAD. 

SIXTH. CONNECT UP YOUR TUBE AND FLASH 
IT TWICE. 

SEVENTH. WASH YOUR HANDS THOROUGHLY. 

EIGHTH. INSERT THE FILM PACKET IN THE 
MOUTH. 

NINTH. REMOVE YOUR FINGERS, AND LET THE 
PATIENT HOLD THE FILM. 

TENTH. READJUST YOUR TUBE-SHIELD IF 
NECESSARY. 

ELEVENTH. AGAIN CAUTION YOUR PATIENT 
TO KEEP ABSOLUTELY STILL. 

TWELFTH. TURN ON THE CURRENT AND MAKE 
THE EXPOSURE. 

114 



THIRTEENTH. REMOVE THE FILM FROM THE 
MOUTH, AND WASH YOUR HANDS AND THE RUB- 
BER PACKET. 

FOURTEENTH. DISCONNECT THE WIRES AND 
MOVE AWAY THE SHIELD. 

FIFTEENTH. STRIP OFF THE RUBBER COVER- 
ING FROM THE FILM PACKET. 

SIXTEENTH. WRITE NUMBER AND NAME ON 
FILM PACKET. 



SEVENTEENTH. 
ENVELOPE. 



PUT FILM PACKET IN 



EIGHTEENTH. PUT ENVELOPE IN LEAD BOX 
TILL READY TO DEVELOP. 

Learn these eighteen steps carefully and always observe 

them as far as possible. The author has found, by the expe- 
rience of many years, that these steps are all necessary and 

should be adhered to in their right order if satisfactory work 
is to be accomplished. 

Particularly in clinic work should these directions be 
insisted on. 



115 



NOTES 



116 



NOTES 



117 



FILM CLAMP 




Figure 21 — (see page lilt) 



118 



CHAPTER XIV. 
Development and Mounting of Negatives 

The development of X Ray films is carried out very much 
the same as with ordinary photographs. The operator who has 
had any experience with amateur developing should find this 
the easiest part of the subject. 

The first requisite is a dark room. This can be a closet 
that has been fitted with a table or wide shelf, about three 
or four feet from the floor, and preferably electric light for the 
dark-room lamp. Red lamps may be purchased from any photo- 
graphic supply store to burn either electricity, oil or candles. 
Running water is also desirable in the dark room, but it is not 
essential, providing you can use it in another room. Dental 
films should not be developed in photographic trays, but 
tumblers or small glass troughs should be used. Three of these 
should be provided. The author has found that the rectangular 
trough-covers of butter dishes, that may be bought in the nearest 
10-cent store, answer admirably, the bottoms of which can be 
used for covers. The films are hung in these dishes, or where 
only two or three negatives are to be developed at a time, 
ordinary tumblers will answer perfectly. Throughout the entire 
operation of developing, fixing, washing and drying, the films 
are held in small clamps that were devised by the author many 
years ago. They may be obtained from the American X Ray 
Equipment Co., of New York. The accompanying illustration 
shows how the film is held in the clamp (Figure 21). Small 
tags are attached to each clamp, on which is written the serial 
number of the radiograph, or even the patient's name. In 
this way the negatives are never mixed up while developing 
several at one time. The operator should have at least a dozen 

119 




Rubij Lamp. 



Water. 



FixinoBaXH. Developer 



Figure 22 — (see page 121) 



120 



of these clamps on hand, and if he expects to do much work 
several dozen will be found very desirable. 

The developer used in dental work is far more concen- 
trated than the ordinary photographic developers. The formula 
that is best to use will be found in the package in which the 
dental films are bought. Different manufacturers of dental film 
advocate different formulae for development. The formula for 
the fixing bath is also given in the direction sheets that accom- 
pany all makes of films. 

The technique for developing is as follows : We will 
suppose that we have taken two radiographs and are ready 
to develop them. We go into the dark room and before shut- 
ting out the white light prepare the solutions and film clamps. 
We take three glass troughs that have been well washed, and 
fill one of them with water and place it as shown in Figure 22. 
Fill another with the developing solution and place it on the 
right, while the third is filled with the fixing bath and placed 
on the left, as shown in the diagram. A towel is also provided 
and placed alongside the troughs on the shelf or table. 

Four clamps are now tagged and the number of the first 
film is written on two of them, while the number of the 
second film is written on the other two. Each pair of clamps, 
with its corresponding film packet, are placed on the shelf 
some distance apart, so that no mistake can be made in the 
dark, and the wrong films placed in the clamps. When 
everything is ready, light the red lamp and put out any other 
white light and close the door of the dark room. Take one 
of the film packets and open it. Take only one of the films 
out, holding the other wrapped in the black paper in your 
hand and place the film in the clamp. Be sure to get the 
sensitive or dull side out, or away from the clamp. The dull 
side can be readily distinguished from the shiny side, by holding 
the film in front of the red lamp and catching the reflection of 
the light on its surface. The dullest reflection is the sensitive 

side. 

121 



FILM MOUNTS 



M. 



CASE NO. 
DATE 



(VIEW ONLY BY STRONG TRANSMITTED LIGHT.} 



UNGUAL ASPECT 



TELEPHONE 
STU YVES ANT 1500 



Dr. F. L, R. SATTERLEE, Jr. 

148 EAST 18th ST.. New York City 



M 



CASE NO.. 
DATE 



(VIEW ONLY BY STRONG TRANSMITTED LIGHT.) 




TELEPHONE 
STU YVES ANT 1500 



UNGUAL ASPECT 



Dr. F. L. R. SATTERLEE, Jr. 

148 EAST 18th ST.. New York C*y 



^MHMBHV 



Figure 23— (see page 123) 
122 



When the first film is in the clamp, hang it in the glass 
trough containing water. Now take the other film from the 
packet you are holding in your hand and place that in the other 
clamp. Hang this also in the water. Take the first film and 
clamp and move it up and down a few times, to be sure that 
the surface is thoroughly wet and that no air bubbles adhere 
to it. Place it in the developing solution on the right. Do the 
same with the second film. 

Observe that the film is whitish and translucent by trans- 
mitted light, when first placed in the developer. Take the films 
out from time to time and hold them up to the red lamp for a 
few seconds at a time only. Watch the image appear on these 
first pictures by occasional inspection. The films are kept in 
the developing bath until, on looking through the film at the 
red light, the whole film looks quite black, and no detail is 
discernible. Then remove the films from the developer, and 
rinsing them by dipping them a few times in the water, transfer 
them to the fixing bath. You can now proceed with the other 
two films in the second packet. Until you are thoroughly 
familiar with the developing operation, it is not well to open a 
second packet till you have the first films in the fixing bath. 
The films are left in the fixing bath until they have cleared as 
much as they will, about ten minutes. They are then taken 
out and hung back in the water bath. After all the films are 
'fixed,' that is, made non-sensitive to actinic rays, the white 
light may be admitted to the room. 

The films are now hung in another large vessel, such as a 
battery jar, or a deep tray, and this is placed under a tap of 
running cold water for about twenty minutes or longer. They 
may then be hung in an empty battery jar to dry, first swabbing 
them ofl very lightly with a small piece of wet absorbent cotton. 
Care must be taken not to dislodge the film from its clamp in 
this operation. Do not fail to immerse the films in water, 
before and after, both the developing and fixing baths. 

W T hen the films are thoroughly dry they are then ready 
for mounting. Figure 23 represents a mount devised by 

123 



the author for dental negatives. These mounts consist of 
rectangles of celluloid, A T / 2 x 2^4 inches. The celluloid being 
clear on one side and dull on the other, resembling ground 
glass. In the center a rectangular border is printed the size of 
the dental picture and slits are punched in the corners of this 
to take the corresponding corners of the film. The film is 
slipped into these mounts film side down. 

On these mounts are printed the necessary blanks to be 
filled in for the recording of the patient's name, the case number 
and date. At the bottom of the mount appears your own name 
and address. Just below the printed rectangle appear the 
words, "Lingual Aspect," and directly above the directions, 
"View only by strong transmitted light." 

These cards can be filed in an index and serve as an 
admirable method for the preserving of the pictures properly 
filled in with the necessary data. When a negative is examined 
by holding it up to a strong light the dull surface of the 
celluloid gives a fine backing and prevents the seeing of objects 
through it, such as the filament in an electric lamp used to 
view it with. Such objects tend to obliterate the detail in the 
picture and confuse the operator* 



* These mounts may be purchased from the Swenarton Stationery Co., of 
New York, printed to order with your name, etc. 



124 



NOTES 




125 




Head-Rest. 



Figure 24 — (see page 127) 



126 



CHAPTER XV. 

Head Pictures on Plates 

There are cases that arise in dental radiography where we 
cannot get the picture on a film in the mouth. For example, 
we may have a patient present with a fracture of the inferior 
maxilla. The jaws may be completely or even partially 
ankylosed, and consequently it will be impossible to get a film 
in the mouth. Again we may have to obtain a radiograph of 
the ramus or even the condyle. In these cases we must take 
the radiograph on a glass plate. 

There are two very good X Ray plates on the market, the 
'Wrattan and Wainwright,' made by the Eastman Co. of 
Rochester, New York, and the 'Ilford' plate, made by the 
Ilford Co. of London. 

These plates can be obtained in both 6 J/2 x 8J4, and 
8 x 10 sizes, the only sizes that we would use. They are 
wrapped in two thicknesses of envelopes, the first black and 
the second or outside one orange colored. This renders them 
lightproof. 

The patient is seated sideways in the chair, with the head 
thrown away back and the involved inferior maxilla pressed 
against the head rest The plate is then slipped between the 
head and the head rest, the pressure of the head against it 
being sufficient to keep it in place. The tube shield is so placed 
as to direct the rays from the opposite side, pointing slightly 
upward, so that the shadow of the maxilla on the opposite side 
just escapes being superimposed on the affected side. It will 
require some little practice to get the right angle every time. 
The accompanying diagram, Figure 24, shows approximately 
the relative positions of the head, the plate and the head rest, 
and the direction of the rays. 

127 



These plates are developed in trays the same as any other 
photographic plates, only using the developing and fixing baths 
the manufacturers recommend in the printed slip that accom- 
panies every box of plates. 

Radiographs should not be made on plates if we can 
possibly show the required area on a film in the mouth. The 
tissues are further from the 'screen,' resulting, therefore, in a 
sacrifice of clearness and detail. Also, we are prone to get 
superimposition of the tissues of the opposite side. Many 
hospitals and radiologists not familiar with the special dental 
technique attempt to take all dental conditions on plates. This 
practice results in the prejudice that many dentists have against 
the resort to radiography in doubtful cases. They have, unfor- 
tunately, only had experience with plates that have been made 
for them by general radiologists without the knowledge of the 
special dental technique, and the finer detail that would have 
been of great assistance was entirely lost. Radiographs on 
plates of conditions of the superior maxilla are particularly 
unsatisfactory. 

Prints of both plate and film negatives are rarely made 
to-day, the dentist preferring to make his diagnosis from the 
negative directly. Printing is a purely mechanical process and 
consequently there must be some loss in the transfer. The 
original negative has more detail than can be obtained in any 
print. All reproductions of radiographs in this book are 
negative reproductions, just as though the actual negative were 
before you (but there is considerable loss of detail due to the 
reproduction). This is done so that the student may become 
accustomed to the X Ray negative appearance of radiographs. 
In the negative dense objects appear white, while the converse 
is true with prints. Plate negatives may be marked with the 
operator's name and its serial number at the time of exposure. 
Small plates of aluminum are stamped with the name, and the 
letters filled in with red lead. Numbers are placed on the 
markers in the same manner. These name plates, or markers, 
are placed on the X Ray plate and are left there during the 

128 



exposure, so that, on development, a radiograph is also made 
of the marker which leaves only the shadow of the letters 
and numbers. 



129 



NOTES 



130 



CHAPTER XVI. 
Dangers of the X Ray 

Shortly after the discovery of the X Ray, it became known 
that many who were exposed to the rays developed a condition 
of the superficial tissues resembling in appearance that of 
sunburn. For some time these effects were not traced to the 
ray itself, but were thought to have been produced by the high 
potential discharge. This theory was, however, soon proved 
to be wrong, and it was found that the rays themselves were 
to blame. Experimenters then became more careful about 
exposing themselves to this powerful agent, that could produce 
these "burns" as they began to be called. Next came the reports 
of more effects of these wonderful rays, such as the falling 
out of the hair, pigmentation of the skin, and the cracking or 
splitting of the finger nails. In fact, in several cases severe 
'burns' were reported and the complete loss of the finger nails. 
These 'burns' were very hard to heal, resisting all means of 
treatment. For awhile these alarming reports threatened to 
entirely discourage the investigators. It was then found that 
these rays, that had the power to produce such changes in the 
healthy tissues, could also be used to advantage in the treat- 
ment of certain pathological conditions of the skin. Interest 
was again aroused, and means were devised by which operators 
could work around these rays with comparative safety. 

Since that time, now many years ago, the entire subject 
has been studied, analyzed and developed, until to-day we are 
no longer working in the dark with an unknown agent, more 
dangerous in its effects than even opium and morphine. 

The effects of the X Ray may to-day be classed under two 
main divisions, primary and secondary. The primary effects 
are due to direct exposure to the rays themselves for a period 

131 



of time sufficient to produce certain changes in the skin known 
as Rontgen Dermatitis. This dermatitis may be of five degrees. 
The first degree resembles a slight sunburn in appearance. 
There is a slight pinkish erythema, dry in character, and with- 
out destruction of tissue. There may be some sensation of 
burning or tingling such as accompanies sunburn. In second 
degree dermatitis there is, in addition, the presence of vesicles 
and the surface becomes moist or weeping. The sensations at 
this stage resemble those of a blistering burn of any character. 
If all exposure to the rays is stopped at this point, the result 
will probably be a slow cleaning up of the condition and a 
slight desquamation, and perhaps a permanent pigmentation. 
Third degree dermatitis is characterized by an angry red 
appearance with intense congestion, which is moist and weeping 
all the time. Upon the raw and sometimes bleeding surface 
there forms a yellowish-white necrotic membrane. This mem- 
brane, however, is made up of only epithelium. The connective 
tissue beneath is not affected, except for more or less swelling. 
If all X Ray exposures were now stopped the condition would 
gradually but slowly subside, and in the course of two or three 
months the ruptured vesicles and suppurating necrotic mem- 
brane would dry up, and would, in turn, be followed by a 
horny epidermis that would appear in spots over the affected 
area. Many cases are considerably retarded by the reappearance 
of the vesicles, and the repetition of this process of throwing off 
and building up sometimes keeps up for months and even 
years. In time, however, the relapses cease, and the permanent 
horny epidermis spreads over the entire area. This new skin 
is quite smooth and natural looking, except for the absence of 
all hairs and follicles. For some time the new coating of the 
epidermis is quite sensitive to external irritations. 

Dermatitis of the fourth degree is characterized by a still 
greater erythema and the degree of congestion is much more 
intense; in fact, the outer coating of the skin becomes mummi- 
fied, in places surrounding actual ulcerations of the lower 
connective tissue. There are great masses of dead tissue 

132 



which, if not removed surgically, will result in gangrene. 
Patients suffering from this degree of dermatitis usually com- 
plain of great pain. In time, if all exposure to the X Ray 
ceases, even this advanced condition of necrotic destruction 
will clear up, but it may take years for the reconstruction to 
take place. In the end the new skin is hard and horny and 
covered in places by scar tissue. 

The fifth degree of Rontgen Dermatitis may be called 
"chronic" dermatitis. It takes place principally on the hands of 
operators, and other workers around the ray, who may be 
exposed, from time to time, over a long period. They are 
continually adding to the effects without getting entirely well 
of the old. The skin becomes thin and atrophic with red 
patches of a vascular nature. There is an entire absence of 
all follicles and hair. Codman, in the Philadelphia Medical 
Journal (1902), describes this condition as follows: "In the 
less pronounced forms the skin appears chapped and roughened 
and the normal markings are destroyed; at the knuckles the 
folds of the skin are swollen and stiff, while between there is a 
peculiar dotting resembling small capillary hemorrhages. The 
nutrition of the nails is affected so that the longitudinal stria- 
tions become marked and the substance becomes brittle. If 
the process is more severe there is a formation of blebs, 
exfoliation of epidermis and loss of the nails. In the worst 
form the skin is entirely destroyed in places, the nails do not 
reappear and the tendons and joints are damaged." 

Other primary effects are the loss of the hair, finger nails, 
and even an acute toxemia with accompanying fever. This 
latter condition is quite rare and only develops where there is 
a marked idiosyncrasy to X Ray reaction. In cases where the 
hair of the head receives the exposure from a low or even a 
medium vacuum tube the hair comes out quite easily from an 
exposure not even long enough to produce a slight erythema 
of the scalp. Hair lost in this manner, however, comes back 
in about six weeks with a fine thick growth, providing the 
exposure was not long enough to destroy the follicles. 



133 



The secondary effects of the X Ray are far more subtle 
in their action than the primary, taking place as they do 
sometimes after a lapse of many years from the time of original 
exposure. First we will mention the development of deposits 
particularly around the knuckles of the hands of X Ray 
workers. These horny excrescences finally develop into hyper- 
keratosis. These keratoses sometimes have an inflamed base 
which, in time, gives way to an epitheliomatous degeneration. 
Epitheliomas developed in this way show no improvement as 
the years go by, and the operator is indeed fortunate if they 
do not spread. There are many cases of carcinoma that have 
for their origin the keratosis on the hands of X Ray workers. 
If these conditions continue to spread, the only way to check 
the depradation is amputation. These cases, however, only 
occur where the victim has repeatedly exposed himself to the 
X Ray and has taken no precautions. Fortunately these cases 
will occur no more, owing to the perfect methods of protection 
practised to-day. The operator who starts to-day to take up 
radiology can proceed without danger, thanks to the knowledge 
we have gained from the unfortunate pioneers who sacrificed 
themselves unknowingly to the cause of science. 

Another secondary effect of the X Rays is its action on 
all embryonic tissue. This action tends to break down and 
destroy the developing cells. Many years after the X Ray 
was discovered it became known that those who had been 
subjected to continual exposures of short duration, in the course 
of their work with the rays, had become sterile, or unable to 
reproduce their kind. This was found to be caused by the 
destruction of the spermatozoa in the male and the primordial 
ovules in the female. The cells involved in these cases were of 
embryonic origin. Sterility produced in this manner is not 
accompanied by impotence. Whether these cases are perma- 
nently affected we are not prepared to say. Some writers 
believe that the condition is but temporary, and its effects will 
pass away as the operator ceases to further expose himself to 
the rays. It is more likely, though, that if the amount of 

134 



exposure has been sufficient or prolonged over a great many 
years that the condition becomes permanent. 

There are numerous other systemic effects that are pro- 
duced, and they differ somewhat in individuals. In some there 
is a tendency to low body-temperature ; as low as 96.3 degrees F. 
has been observed as a normal temperature of a pioneer 
investigator. 

The student reading of these effects of the X Ray should 
not become frightened and hesitate to use this wonderful 
diagnostic agent. He should, however, fear the ray and respect 
it to the extent of carefully following a technique of protection 
that insures him against its casualties. With the modern 
method of procedure the protection is complete, and the opera- 
tor should never be subjected to any exposure at all. Because 
we know that sulphuric acid is a deadly and caustic liquid we 
are not afraid to keep it properly bottled for use. As long as 
we know the danger of the X Ray, we reduce the possibilities 
of the deleterious effects. 

The danger to the patient exposed to the X Ray is prac- 
tically nil. Radiographs of all parts of the body are to-day 
made with the improved apparatus in but a few seconds at 
the most. This short exposure is not sufficient to produce the 
slightest effect, either primary or secondary. 

Instruments have been devised to measure the dosage of 
the X Ray. Perhaps the most used is the Radiometer of 
Holznecht. By means of this device the rays emanated from a 
vacuum tube for the purpose of therapeutic application, or 
even for the taking of a radiograph, can be measured by its 
chemical effect upon a prepared pastil exposed simultaneously. 
This chemical pastil changes color during its exposure to the 
rays and the shade of color is compared with a scale devised 
by Sabouraud. 

The intensity of the rays is measured in units called 
Holznecht's units, or as they are generally spoken of as H's. 
For example, the dose necessary to produce the slightest 
erythema on the face of an adult is equivalent to three of the 

135 



Holznecht units, or 3H. Now the greatest dose necessary for 
the taking of a radiograph is but a small fraction of a single 
H unit. From this you will see the enormous margin of safety 
under which we are working in the exposure of our patients. 
If to-day an erythema is produced on a patient, from the effect 
of the exposure employed for the taking of a radiograph, it is 
due entirely to the faulty technique of the operator. There 
is no excuse for such a thing happening, even where there is 
a marked idiosyncrasy toward X Ray effects on the part of 
the patient. 



136 



RADIOGRAPHS 




Figure 26 — (see page 177) 



155 




156 




157 




Figure 29 — (see page 1S1) 




Figure 30 — (see page 183) 
158 




Figure 31 — (see page 184) 




Figure 32— (see page 184) 
159 




Figure 33 — (see page 184) 




Figure 34 — (.see page 1S5) 
160 



Figure 35 — (see page 185) 




Figure 36 — (see page 185) 
161 




Figure 37 — (see page 1S5) 




Figure 38 — (see page 1^5) 
162 




Figure 39 — (see page 185) 




Figure 40 — (see page 185) 
163 




Figure 41 — (see page 1S5) 




Figure 42 — (see page 1S5) 
164 




Figure 43 — (see page 185) 




Figure 



-(see page 186) 
165 




Figure 45 — (see page 186) 




Figure 46 — (see page 1S6) 
166 




Figure 47 — (see page 186) 




Figure 48 — (see page 187) 

167 




Figure 49 — (see page 1ST) 




Figure 50 — (see page 1ST) 

168 




Figure 51 — (see page 187) 




Figure 52 — (see page 187) 
169 




Figure 53 — (see page 187) 




Figure 54 — (see page 1ST) 

170 




Figure 55 — (see page 187) 




Figure 56 — (see page 187) 
171 




Figure 57 — (see page 187) 



172 




173 



DENTAL RADIOSCOPE 




Figure 59 — (see page 193) 



174 



DENTAL RADIOSCOPE (Sectional View) 



H 




L 



H 



Figure 60 — (see page 193) 



175 



CHAPTER XVII. 
Reading the Negatives 

In order to properly translate the findings of a dental 
radiograph we must first become familiar with the normal 
appearances of the several tissues involved in the dental 
anatomy, as shown in the X Ray negative. 

The dental radiograph we have defined as 'a shadowgraphic 
representation of the tissues, taken in a series of planes from 
facial to lingual surface.' We therefore have to read the 
condition presented in the negative by the shadows they throw, 
and in most cases to read through the superimposed tissues. 
All tissues are represented by a certain intensity of shadow, 
governed by the corresponding density of the actual part. In 
the negative dense tissue is characterized by white areas, while 
tissues less dense are shown by darker appearances. Absence 
of tissue is indicated by black portions of the negative. 

Figure 26 represents a dental radiograph enlarged to twice 
the actual size, and shows the normal X Ray appearances of 
the tissues. We will start with the lightest area shown, as 
'A/ which represents an amalgam filling in the crown of the 
first molar tooth. The next lighter shade is seen in the crowns 
of the teeth themselves, as 'B.' Then we find the shadow 
getting darker as the density of the tooth structure becomes 
less, as 'C representing the roots of the teeth. Next comes 
the thicker portions of the process 'D,' and then the white line 
'E,' which borders the sockets of the roots. This tissue repre- 
sents the most recently developed portion of the alveolar wall, 
and is made up of heavier deposits of lime salts. 'F' marks 
the grade of density shown by the white lines that represent 
the divisions between the interstices of the alveolar process. 
All cancellous bone tissue is characterized in its X Ray appear- 
ance by this whitish network structure. The next gradation 
of density is shown by the appearance of the pulp chambers 

177 



and canals of the several teeth 'G.' The pulp itself being 
essentially soft tissue is not shown in the radiograph, but the 
space occupied by soft tissue is outlined by dark areas. This 
is also illustrated by the space occupied by the periosteum, or 
peridental membrane, lining the tooth sockets shown by the 
line 'H' surrounding the roots. The compact bone tissue 'K' 
is in this case shown as having little density. This dark 
appearance in the radiograph is caused by the very thin structure 
of the inferior maxilla at this point. This degree of density 
varies greatly in individuals, and no approximate gradation of 
shade can be established to characterize the normal appearance 
in all cases. We can also see a still darker line running through 
the compact bone tissue and parallel to the lower border of the 
maxilla. This dark line, %,' is the inferior dental canal. The 
blackest part of the picture is the area, 'M/ which represents 
the complete absence of tissue, as shown by the spaces between 
and above the crowns of the teeth. 

This radiograph, as shown in Figure 26, should be care- 
fully studied and compared with Figure 27, which represents 
a still greater enlargement from the same negative. These 
various gradations of density should be borne in mind con- 
stantly as representing the normal X Ray appearances of the 
dental tissues. Now turn to Figure 28 and observe how these 
comparative densities will appear in the actual size radiograph 
without enlargement. In practice you will have to make your 
diagnosis from this small normal-sized picture; therefore it 
would be well to compare it carefully with the two enlarge- 
ments from the same negative. All other radiographs illus- 
trating the various pathological conditions we will reproduce as 
negatives enlarged to twice the size, for the purpose of amplify- 
ing the finer detail that might be lost in the process of book 
reproduction.* In stating that these enlargements are twice 



* It is absolutely impossible, with printer's ink, to faithfully reproduce all 
the fineness of detail and contrast that we can see on the translucent negative 
viewed by transmitted light. The twofold enlargement of the negatives serves to 
bring out, to a certain extent, the finer lines of detail, but owing to the additional 
process, there is a corresponding loss of contrast or gradation between light and dark 
areas. As these radiographic negatives are reproduced primarily for the instruction 

178 



the size of the original negative it must be understood that 
each dimension of the picture is twice as large, although the 
actual area of the radiograph is four times as great. 

The next important step, after differentiating between the 
shadows that indicate the densities of the several parts of the 
dental negative, is to correctly get our bearings in regard to 
the teeth we are looking at, and their positions relative to the 
part of the mouth in which they are situated. This is called 
'orienting' the picture. The reproductions in this book are 
the same as though we looked through the glossy or non- 
sensitive side of the film, and represents the lingual aspect of 
the teeth and surrounding tissues in all cases. From this we 
will note that in the first radiograph we show, from left to 
right, the third, second and first molars, and part of the 
second bicuspid of the inferior left maxilla. Another fact that 
we must consider in the translation of the radiographs, is that 
in some cases only two or three teeth in the center of the 
picture show very clearly, while the others, particularly those 
at the edges of the film, are more or less indistinct. This is 
caused by the curvature of the arch which brings two or three 
teeth directly in the field of the rays, while the others are more 
or less superimposed on each other, or else are distorted by 
the curvature of the film conforming to that of the palate, and 
so destroying the uniformity of the angle that the direct rays 
from the tube, form with the film. 

We have seen how the various gradations of density of 
the several parts may be compared on the individual radiograph, 
but these gradations in one picture cannot be compared with 
the relative densities of another, which may have been taken 
under different conditions of penetration in the X Ray tube. 
A slight difference in degree of vacuum in the tube will give 
marked variations in the relative contrasts of two pictures. 



of the student, the author has permitted, in a few cases, a certain amount of 
retouching of these enlargements, under his personal supervision, to- the extent only 
of strengthening the contrasts between light and dark areas, so that they may 
approach the actual gradations seen in the original negative. In no case has detail 
been inserted or gradations brought out that could not be seen in the original film. 

179 



NOTES 



180 



CHAPTER XVIII. 
Diagnosis of Pathological Conditions 

Having considered the normal appearance of the dental 
tissues under the X Ray, we will now turn our attention to the 
variations from the normal that we meet with in the presence 
of pathological conditions. Let us first consider a typical case 
of alveolar abscess. Where an abscess takes place in the 
alveolar process, we always have an accompanying destruction 
of cancellous bone tissue. From our consideration of the nor- 
mal picture we have learned that absence of tissue is charac- 
terized on the radiograph by dark areas. We, therefore, must 
look for a dark area in the case of an alveolar abscess. Let us 
examine Figure 29 (Case I.). Here we see, from left to 
right, the superior left first bicuspid, cuspid and lateral incisor 
teeth. We note that the bicuspid is capped, the gold crown 
showing very white, owing to its density, and we also observe 
that this cap does not accurately fit the crown of the tooth. 
Above the gold cap is seen a white line running upward in the 
root canal and extending about two-thirds of the way to the 
apex. From its whiteness we judge that it must be some very 
dense substance, and we come to the conclusion that it must 
be filling material. Note particularly that, the apical end of 
the canal is not filled, and then observe the circumscribed dark 
area in the alveolar process surrounding the apex of the root. 
This dark area indicates lack of density or absence of tissue. 
In this case the density of the process should be homogeneous, 
therefore we are led to believe that an actual cavity (to account 
for the absence of tissue) must exist. It is too small and too 
low down to be the maxillary sinus, therefore we are led to 
believe that its existence must be due to some pathological 
condition. Where these dark areas are found in the alveolar 

181 



process, and are not natural cavities, such as the antrum and 
the nasal cavities, and where they are markedly circumscribed, 
that is having a distinct and abrupt line of demarkation between 
the dark area and its surrounding tissue, we can, in nearly 
every case, make the positive diagnosis of alveolar abscess. 

If the abscess cavity contains any quantity of pus the area 
is generally particularly dark. This is caused by the fact that 
pus has been found to be fluorescent under the influence of the 
X Ray. This fluorescence increases the radiations that affect 
the film in this particular area, consequently producing a greater 
reaction on the sensitive emulsion, which shows on the negative 
as accentuated dark areas. From this we deduce the fact that 
in many cases where the area is particularly black the abscess 
cavity will probably contain pus. 

In the case in question (Figure 29) we note that the area 
is circumscribed and that it is decidedly dark as compared 
with the normal tissue. We can safely say that in this case 
we have a well-developed alveolar abscess that is quite active. 

The etiology of this abscess is also quite apparent and, 
furthermore, was borne out by the clinical history. The patient, 
a Mr. D., presented at the Clinic, with intense pain, over the 
region of the bicuspid that had recently been capped. The 
radiograph was taken and the diagnosis of alveolar abscess was 
at once made certain. The cap was removed, the filling material 
drilled out, and drainage established through the apex. The 
pain disappeared and the condition commenced to improve. 
After the canal had been open for some days and the active 
process subsided, the canal was again filled, but this time to 
the apex, and the cap once more replaced. 

In this case the pulp had been devitalized, and in the 
removal some of it was left at the apical end of the canal. 
This portion of the dead pulp was sealed in by the filling 
material that partly filled the canal, with the result that the 
gases of putrefaction were given off and forced through the 
apical foramen, starting up an inflammation of the perice- 
mentum. If a radiograph had been taken at this stage just a 

182 



slightly enlarged portion of the dark line surrounding the root 
would be apparent at the apex. Pericementitis may be deter- 
mined by the X Ray, even before the patient feels any real 
pain. In the case in question the pericementitis was not taken 
care of, and the condition went on to the stage of abscess with 
its consequent destruction of tissue, and the formation of pus, 
before the patient presented for treatment. If radiographs were 
taken from time to time after an abscess area has been 
evacuated and drained, the process of repair will be seen. At 
first a distinct whitish line will be noted surrounding the area 
of destruction. This line indicating increased density, probably 
represents an extra deposition of lime salts over the walls of 
the abscess cavity, being an effort of nature to check the further 
destruction of cancellous bone tissue. Granulation would then 
be noticed by the slightly whitish tint inside the white line 
of demarkation. This would gradually fill in toward the center 
of the cavity, and the shade would get lighter and lighter as 
the density of the tissue increases. As osseous tissue in time 
develops, the density of the abscess area more closely resembles 
the healthy tissue adjacent to it, and, in fact, ultimately takes 
on the characteristic network appearance of the normal alveolar 
process. 

Before leaving Figure 29 we will call attention to the 
absorption of the alveolar process consequent to the extraction 
of the second bicuspid and molar teeth. 

Case II., Figure 30, represents another typical case of 
alveolar abscess surrounding the apex of the superior left 
lateral incisor tooth. In this case the pus sac has ruptured 
and the pus has infiltrated into the surrounding process as 
indicated by the slightly darker appearance extending down- 
ward toward the roots of the bicuspid and central incisor teeth. 
This darker appearance is caused in all probability by the 
fluorescence of the pus, and not to any destruction of tissue. 
If the condition were allowed to go on, however, necrosis would 
inevitably set in. The cause of this abscess is the same as in 
Case I., and the partial root filling is to be particularly noted. 

183 



Case III., Figure 31, shows another abscess on the distal 
root of the inferior right second molar. Again, note the piece 
of filling material just at the opening of the distal root canal. 
The operator in this case was under the impression that the 
root had been perfectly filled! 

Case IV., Figure 32, represents another alveolar abscess 
involving the superior left central and lateral incisor teeth. 
In this case the repair is taking place and the root canals are 
refilled. Note the appearance of the filling-in tissue, the only- 
very dark area remaining, being directly around the root of the 
central. Above the abscess area there appears a white line 
running obliquely downward toward the median line, with a 
dark area to the right of it, and one to the left of it higher up. 
The former area represents the nasal cavity and the latter the 
anterior part of the left maxillary sinus. The white line is 
the floor of the nasal cavity. Note the increased density of the 
maxillary suture. At the apex of the right central we see a 
slightly dark area, indicating the presence of an inflammation 
of the periosteum. This is hardly large enough to be classed 
as an abscess. 

Case V., Figure 33, shows an active abscess in the socket 
of the superior left lateral incisor tooth, which has been 
extracted. A slight involvement of the apex of the cuspid is 
also seen. Above the bicuspid region you will note two dark 
areas surrounded by a white line. These areas represent two 
chambers of the antrum cavity, the white lines indicating the 
exterior walls, the shadows of which are thrown downward 
and superimposed over the alveolar process. The dark area 
inside denotes the normal antrum cavity. The heavier white 
line above represents the osseous tissue dividing the posterior 
floor of the nasal cavity and the hard palate. Note that the 
antrum cavity is seen to extend above this white line, due to 
the superimposition of the shadows. This representation of the 
antrum cavity is seen quite frequently in the radiograph and 
great care and judgment must be exercised not to misinterpret 
the normal antrum cavity for large filling-in abscess areas. 

184 



Cases VI. and VII., Figures 34 and 35, present two more 
typical radiographs of alveolar abscess where the destruction 
has been great. In Case VII. we observe an involvement of 
the nasal cavity with a communicating sinus. 

We will now consider some cases of necrosis. Case VIII., 
Figure 36, is particularly interesting, since it shows on the one 
picture the radiographic difference between abscess and necrosis. 
On examination the radiograph presents a large abscess cavity 
involving the roots of the superior right central and lateral 
incisors and the cuspid teeth. The upper or palatal portion 
gradually shades off from dark to light, while the lower portion 
shows a distinct line of demarkation. The upper portion is 
necrotic ! This constitutes the difference. Where there is an 
accompanying death of tissue the process becomes thoroughly 
infiltrated with pus, and a condition that might be termed 
rarefying ostitis obtains. The gradation of shadow between the 
healthy and the necrotic bone structure becomes less and less 
apparent. We may say that wherever we observe dark areas 
gradually shading into lighter ones THE CONDITION IS 
CHARACTERISTIC OF NECROSIS. Note also in Figure 36 
that the apex of the central root is absorbed. 

Cases IX. to XIV., inclusive (Figures 37 to 42, inclusive), 
are all typical necrosis cases. They should be well studied and 
compared with the series on alveolar abscess just preceding. 
Figure 41 (Case XIII.) shows a necrotic condition of the 
maxillary suture. 

Case XV., Figure 43, presents an interesting study of 
maxillary sinusitis. Almost the entire antrum is shown in this 
radiograph. The fistula connecting the antrum with the old 
abscess cavity that is still active in the center is well shown, 
as well as the extensive necrosis inside the antrum, and of the 
process. 

One of the foremost uses of the radiograph to the dental 
surgeon is its application to the study of root canal fillings. 
It would surprise the average dentist to see the result of a 
hundred radiographs of root fillings made by some of the best 

185 



men in the country. In many cases, where the operator believes 
that he has reached the apex, a radiographic view of his work 
would prove to him that this is not the case. The author 
firmly believes the time is coming, and perhaps not so far 
distant, that every reputable dentist will ascertain by this abso- 
lutely sure method of investigation the result of each root 
filling he makes. Let us examine a few cases taken at random 
from the author's collection. Some of these were from cases 
made by students of the clinic, while others were from estab- 
lished practitioners. The reader may judge for himself which 
cases belonged to the former and which to the latter. 

Case XVI., Figure 44, represents the perfect filling of an 
inferior second bicuspid. This filling, moreover, is a gold filling, 
and extends, as you will see, clear down to the very apex 
of the root. Unfortunately we do not meet with many cases 
where this result is obtained. 

Let us contrast the last case with Case XVII., Figure 45. 
Here we see that the operator has succeeded in reaching the 
apex of the lateral root, and has even gone beyond. The result 
of this overzealousness is observed when we examine the 
rarefying ostitis surrounding the root. Also note the extent 
of the cuspid filling. In the first bicuspid we see a curved 
apex and a faint white, narrow line extending nearly to the 
apical foramen. This is the remains of a broach which had 
been left there during the extraction of the pulp, and the filling 
material placed in the canal on top of it. 

Case XVIIL, Figure 46, represents a case where a piece 
of an instrument has been left in the canal of a superior right 
central incisor. Furthermore, in the effort to remove this 
foreign body from the canal, the side of the canal has been 
perforated and an active abscess developed as seen in the 
picture between the central and lateral incisors. The perforation 
is not discernible in the radiograph, since it is in a plane at 
right angles to the direction of the rays. 

Case XIX., Figure 47, shows how a perforation may be 
found by the radiograph. A wire is passed up into the canal 

186 



and the exposure made while it is temporarily held in place 
with a gutta-percha seal. The abscess resulting in this case 
is well shown. 

Case XX., Figure 48, shows where two wires are sealed 
in the root canal for the ascertaining of a perforation, and to 
see if the apex of the canal has been reached. 

Case XXI., Figure 49, is another example of perforated 
root canal, with a large quantity of filling material pushed 
through into the process. The result is apparent. 

The shadows cast by filling materials vary but little in 
their relative gradations. Oxychloride, gutta-percha and 
cement have about the same density when used as root-filling 
material. Gold and amalgam cast slightly whiter shadows. 
'Mummifying Paste' has about the same density as the tooth 
structure itself, consequently a canal so filled appears as a 
root without a canal. 

Case XXII., Figure 50, shows the radiographic appearance 
of normal unerupted teeth in the mouth of a child. Note that 
in the unerupted teeth the roots have not yet developed. 

Case XXIII. , Figure 51, represents the impaction of two 
molars, crown to crown, against each other. 

Case XXIV., Figure 52, shows a central incisor erupting 
at right angles to its normal axis. 

Cases XXV. and XXVI., Figures 53 and 54, show a 
superior first and second bicuspid, respectively, erupting upward. 
This is rather an unusual position for impacted bicuspids. 

Case XXVII., Figure 55, is a very rare type of inferior 
first molar impaction. Note as well that the third molar which 
can just be seen at the extreme left of the radiograph is also 
impacted against the second molar. 

Cases XXVIII. and XXIX, Figures 56 and 57, illustrate 
another class of cases where the X Ray is of the greatest use 
to the dentist. This is where there are old roots left in the 
alveolus after extraction, and remain there, often unsuspected 
by the patient for years, till, at length, through the absorption 
of the process, their ragged edge digs into the gum tissue and 

187 



causes great discomfort. Their extraction is often very difficult 
without the aid of a radiograph, and is accompanied by the 
injuring of an unnecessarily large amount of gum tissue in the 
effort to locate them after the gum has healed over. 

The foregoing twenty-nine cases are but examples of many 
that might be cited to demonstrate the usefulness of the ray 
to the up-to-date dentist. But it was not the intention of the 
author to reproduce these radiographs for that purpose, but 
rather to serve as a type of the more important classes of 
cases, and to show the student of the subject how to go about 
their proper translation, to the end that they may become used 
to the reading of these X Ray shadows and so make more 
accurate diagnoses of conditions. We might go on illustrating 
cases, ad libitum, where new and interesting conditions present, 
but the author prefers in this volume to limit these cases to 
the ones already shown, rather than to flounder in an unending 
sea of radiographs, the explanation of which could not possibly 
be contained in this present text book. At some future time, 
however, the author hopes to present to his readers another 
volume dealing more specifically with individual cases. 

Figure 58 represents a radiograph of the head taken on a 
glass plate. Note particularly how well the inferior dental 
canal and foramen are shown. This picture was made by the 
author with an exposure of twenty seconds, at a distance from 
anode to plate of twenty-eight inches (the maximum distance 
that would be used), while testing the new standard dental outfit 
manufactured by the American X Ray Equipment Co. of 
New York. 



188 



NOTES 



189 



NOTES 



190 



CHAPTER XIX. 
Stereoscopic Radiographs of the Teeth 

Stereoscopic radiographs of the teeth and adjacent tissues 
were first made and shown by the author in 1905. Since that 
date little has been done with them owing to the difficult 
technique involved. 

There are many cases where it is very desirable to separate 
the superimposed planes of the ordinary radiograph. For 
example, suppose we have a picture showing two roots directly 
superimposed on each other, a very frequent occurrence, and 
let us further suppose that an abscess area is shown pointing 
upward from the apices of the roots. The natural question 
that arises is, from which root does the abscess originate? It is 
impossible to positively determine this from the flat single pic- 
ture, but if we make stereoscopic radiographs of the condition 
and view them through a stereoscope the teeth stand out and 
take on the rotundity that they would have if actually viewed 
by the eyes in the dissected jaw. In other words, we would 
appreciate the several planes separately, and objects would 
appear to have all three dimensions. The original stereoscopic 
radiographs made by the author eight years ago were printed 
positives and viewed with the ordinary photographic stereo- 
scope. The difficulty in the technique of making these pictures 
was twofold. First it was essential to take two radiographs 
of the teeth to be examined, from two viewpoints separated the 
normal distance that we have between the pupils of the eyes. 
To do this we had to move the X Ray tube just two and a 
half inches (the average pupilary distance) in a lateral plane 
between the exposures, at the same time preserving the same 
relative position with regard to all other planes. Secondly, we 
had to remove the first film from the mouth and substitute the 
second for the dual exposure, the second film having to be 

191 



placed in exactly the same position with regard to the tissues 
as the first. 

The author has recently perfected a comparatively simple 
technique for the overcoming of these heretofore difficult fea- 
tures. A small plumb-bob is suspended from one of the 
terminals of the tube shield and this is allowed to hang freely 
directly over a yardstick that is mounted in a horizontal plane 
coinciding with the plane in which the tube must be moved 
during the exposure. The first picture is taken, and the tube 
shield moved along till the plumb-bob has traversed just two 
and a half inches on the yardstick and the second exposure 
made. To insure the placing of the second film in the abso- 
lutely same position as the first, an impression of the part of the 
superior arch that we wish to radiograph is first made with 
wax on a 'bite-plate/ and while the wax is still soft the film 
packet is pressed into the impression in the proper position 
until it leaves an indentation. The film packet is then removed, 
the wax chilled, and the film packet replaced. The whole im- 
pression with the film is then replaced in the mouth, the patient 
getting the same bite and the first exposure made. The second 
exposure is made in the same way, the second film packet being 
placed in the same indentation in the wax. This same pro- 
cedure can be carried out with the lower arch by the use of a 
partial impression tray with the outer wall cut away. These 
bite plates and impression trays may be obtained from the 
S. S. White Co. of Philadelphia. 

This method of holding the film in the mouth may be 
used as well for ordinary radiographs in cases where there is 
difficulty in the patient holding it. 

The author has also recently improved the old method of 
viewing the stereoscopic radiographs. Formerly it was neces- 
sary to print and mount the stereoscopic pictures before they 
could be placed in the stereoscope, but now the negatives are 
used themselves. They are placed in an instrument that the 
author has termed a dental 'Radioscope.' This is illustrated 
in Figures 59 and 60. 

192 



Figure 59 represents an actual photographic view of the 
instrument, while Figure 60 shows the interior construction 
being a top view with the cover removed. A light tight 
viewing box is constructed with two mirrors, C and D, mounted 
at right angles to each other. The two stereoscopic films are 
mounted in the regular dental celluloid mounts and are 
respectively inserted in slots and grooves at either side of the 
mirrors, as A and B. The films, when so inserted, coming 
directly in front of two windows, F and G. The film on the 
right is capable of fine adjustment by the set screw K for 
lateral movement, and another set screw on the cover of the 
box (shown in Figure 59), which presses against the spring L 
for vertical adjustment. The lamps, H, at either end of the 
box are lighted, and the observer looks through the hood E. 
The right eye sees the reflection of the right negative in the 
mirror, D, through the lens, Y, while the left eye sees the 
other negative in the mirror, C, through the lens, X. The 
negatives are equally illuminated by the lamps, and if we 
manipulate the fine adjustment screws till the images of the 
two radiographs register perfectly, we will perceive a perfect 
stereoscopic aspect of the combined negatives. The hood, E, 
can be moved in or out till the focus of the lenses are adjusted 
to suit the eyes of the observer. 

Radiographs taken and viewed in this manner show far 
more detail than the ordinary negatives, and in obscure cases 
should always be resorted to if the operator wishes to give his 
patient the benefit of the best means of diagnosis obtainable. 
In developing these pictures care should be taken to develop 
them an equal length of time so that they will have the same 
relative density. The same is true for the original exposure. 
While this book is going to press, the author is working 
on a new method by which he has succeeded in doing away 
with the double exposure altogether. When this method, which 
the author has termed "the radioscopic method of examination," 
is perfected it should so simplify the making of these pictures 
that they may be employed in every routine case. 

193 



NOTES 



194 



CHAPTER XX. 
Conclusion 

In the preceding chapters the author has tried to bring 
before his readers the entire subject of Dental Radiology in 
as clear and at the same time comprehensive a manner as 
possible through the medium of text and illustrations. There 
are many points, however, that are hard to explain by these 
means. Particularly is this true in regard to the coloration of 
the X Ray tubes. It will be only with experience that the 
operator can gain the ultimate success for which he is working. 
At the same time the cloak of mystery 'that has for so long 
enshrouded the X Ray and all pertaining to it has been steadily 
shrinking, till we can at last say that it is a working science. 
The author has endeavored to give, throughout the book, the 
benefit of all 'short cuts' and discoveries that he has worked 
out in a practice of over twelve years, particularly devoted to 
the study of the dental aspect of Radiology. 

Students of this subject should pay particular attention 
to the precautions that should be taken to make its practice 
both safe and harmless. It is a wonderful agent that has been 
placed at our disposal, but it should not be abused. It has its 
limitations like every other branch of science, but properly 
and safely used it can do a great deal of good to suffering 
humanity. 

Before closing it would seem desirable to give to the 
student starting out in the practice of Dental Radiology a few 
hints and suggestions as to what not to do. 

DON'T EXPOSE YOURSELF UNDER ANY CONSIDERA- 
TION TO THE X RAYS. 

DON'T ALLOW YOUR PATIENT TO SIT IN THE PATH 
OF THE RAYS WHILE YOU ARE TESTING TUBES. 

195 



DON'T KEEP YOUR PATIENT IN AN UNCOMFORT- 
ABLE POSITION WHILE YOU ARE ADJUSTING 
YOUR TUBE. 

DON'T BE TOO SURE OF THE RESULT OF THE 
PICTURE. 

DON'T MAKE TOO BIG CLAIMS FOR YOUR KNOWL- 
EDGE OF RADIOGRAPHIC DIAGNOSIS. 

DON'T HOLD FILMS IN THE MOUTH YOURSELF. 

DON'T TRY TO COVER TOO LARGE AN AREA WITH 
ONE FILM. 

DON'T USE PLATES IF YOU CAN GET THE AREA 
ON A FILM IN THE MOUTH. 

DON'T USE OLD FILMS OR DEVELOPER. 

DON'T LEAVE YOUR FILMS WRAPPED TOO LONG 
IN RUBBER. 

DON'T FAIL TO PRESERVE A COPY OF YOUR 
NEGATIVE. 

DON'T FAIL TO NUMBER AND FILE ALL THESE 
COPIES. 

DON'T ABUSE YOUR TUBE; LET IT REST OCCASION- 
ALLY FOR A WEEK AT A TIME. 

DON'T ATTEMPT TO TAKE PICTURES OF OTHER 
PARTS OF THE BODY FOR PATIENTS UNLESS 
YOU HAVE HAD INSTRUCTION. 

DON'T TRY TO DRY YOUR NEGATIVES BY HEAT 
OR IN THE SUN. 

196 



DON'T TAKE A RADIOGRAPH OF A PATIENT UN- 
LESS THERE IS A WITNESS IN THE ROOM. 

DON'T TAKE RADIOGRAPHS OF PATIENTS FOR 
RIDICULOUSLY LOW FEES. BETTER TAKE IT 
FOR NOTHING THAN TO UNDERESTIMATE YOUR 
SERVICES. 

DON'T CHARGE PROHIBITIVE FEES, EITHER. 

DON'T FAIL TO THOROUGHLY UNDERSTAND THE 
WORKING OF YOUR APPARATUS. 

DON'T STORE YOUR FILMS AND PLATES WHERE 
THEY MAY POSSIBLY RECEIVE X RAY EXPOSURE. 

DON'T FAIL TO SWAB OFF YOUR NEGATIVES AFTER 
WASHING WITH ABSORBENT COTTON. 

DON'T ALLOW ANYONE TO GET NEAR THE CON- 
DUCTING WIRES WHILE THE APPARATUS IS 
WORKING. 

DON'T HANDLE A WET NEGATIVE ANY MORE 
THAN NECESSARY. 

DON'T FAIL TO TAKE A RADIOGRAPH IN EVERY 
CASE WHERE YOU THINK IT WILL BE OF BENE- 
FIT TO YOU OR YOUR PATIENT. 



the end. 



197 



NOTES 



198 



NOTES 



199 



NOV 4 1913 



